Semiconductor device and production method therefor

ABSTRACT

The invention is characterized by attaining a lower dielectric constant and including an inorganic dielectric film which is formed on the surface of a substrate and has a cyclic porous structure having a pore ratio of 50% or higher.

FIELD OF THE INVENTION

[0001] The invention relates to a semiconductor device and a method formanufacturing the same, and more particularly, to an inorganicdielectric film of low dielectric constant.

BACKGROUND

[0002] Lowering the dielectric constant of an interlayer dielectric filmis an important challenge to be met for making a semiconductor devicefaster and reduce power consumption. Various ideas have been implementedwith a view toward lowering a dielectric constant.

[0003] In order to lower a dielectric constant of the interlayerdielectric film of a related-art semiconductor device, the followingmethods have been put forward:

[0004] (1) a method for doping a silica film, which is an inorganicdielectric film, with fluorine;

[0005] (2) a method for forming an organic dielectric material having alow dielectric constant as a base material; and

[0006] (3) a method for intentionally forming a porous film.

[0007] However, in the case of the method defined in (1), a silica filmcan be doped with fluorine on the order, at most, of a few percentagesin element proportion, because the heat resistance of the dielectricfilm is deteriorated. Therefore, there arises a problem of thedielectric constant being lowered by only 10% to 15% from the dielectricconstant of the related-art silica-based interlayer dielectric film.

[0008] In the case of the method defined in (2), the moisture resistanceof the base material is considerably deteriorated as compared with thatof the related-art silica-based interlayer dielectric film, because thebase material is an organic material, thereby leading to occurrence of aproblem of a decrease in reliability of a semiconductor element.

[0009] In the case of the method defined in (3), since a porousstructure is random, the mechanical strength of the interlayerdielectric film will be deteriorated remarkably. Hence, thesemiconductor element is vulnerable to fracture when being packaged,which is responsible for the decrease in the reliability of thesemiconductor element.

[0010] In many cases, a porous structure is not closed. If the porousstructure is not closed, the moisture resistance of the interlayerdielectric film will be decreased remarkably, which in turn induces adecrease in the reliability of the semiconductor element.

[0011] Moreover, as further miniaturization of the semiconductor deviceand realization of a still higher packing density are pursued,inter-wiring capacitance and inter-wiring-layer-capacitance pose seriousproblems.

[0012] As mentioned above, the related-art dielectric film suffers froma problem of the inability to sufficiently reduce a dielectric constantand a problem of insufficient mechanical strength.

SUMMARY OF THE INVENTION

[0013] The invention has been conceived in light of the foregoingcircumstances and aims at providing a dielectric film having a lowdielectric constant and high mechanical strength.

[0014] The invention also aims at providing a semiconductor devicecapable of diminishing capacitance existing between wiring layers andinter-line capacitance even while attaining miniaturization and tighterpacking of a semiconductor device.

[0015] Accordingly, the invention is characterized in that asemiconductor device comprises an inorganic dielectric film which isformed on the surface of a substrate and has a pore ratio of 50% orhigher.

[0016] Since the dielectric constant of air is low, by means of such aconfiguration the dielectric constant of the dielectric can be reducedfurther as compared with that achieved when the dielectric film is dopedwith fluorine. Hence, the dielectric constant of the dielectric film canbe minimized.

[0017] Preferably, the invention is characterized in that the inorganicdielectric film is formed on the surface of the substrate, and the poreshave an orientation characteristic.

[0018] According to the configuration, the pores possess the orientationcharacteristic. Hence, mechanical strength of the dielectric film can beenhanced, and a dielectric film of high reliability can be obtained.

[0019] Preferably, the invention is characterized by further comprisingan inorganic dielectric film which is formed on the surface of thesubstrate and has periodic porous structures of two or more types.

[0020] Since the dielectric constant of air is low, by means of such aconfiguration the dielectric constant of the dielectric film can bereduced further. The dielectric constant of the dielectric film can beminimized. Since the dielectric film has a plurality of types of cyclicporous structures, opening sections of the pores can be closed by meansof the domains. As a result, the mechanical strength of the dielectricfilm can be enhanced, and a dielectric film of high reliability can beobtained.

[0021] More preferably, the invention is characterized in that theinorganic film has repeated arrangement of a first porous structuredomain having periodically-arranged columnar pores and a second porousstructure domain having layered pores cyclically arranged in a directionperpendicular to the surface of the substrate.

[0022] According to such a configuration, the first porous structuredomain having periodically-arranged columnar pores and the second porousstructure domain having layered pores periodically arranged in adirection perpendicular to the surface of the substrate are repeatedlyarranged. Particularly when the dielectric film is used as an interlayerdielectric film, the pores can assume a closed structure in which noopening sections are provided for upper layer wiring or lower layerwiring. Hence, the dielectric film plays the role of a low dielectricthin film having superior moisture resistance and enhanced reliability.Further, a uniform electrical characteristic can be achieved.

[0023] Moreover, the porous structure is oriented in a differentdirection in each domain. Hence, the opening sections of the pores canbe closed by each other. There can be obtained a low dielectric thinfilm having superior moisture resistance substantially equal to that ofa dense film, superior mechanical strength derived from a cyclicstructure, and an ultimately low dielectric constant. An interlayerspace is supported by adjacent layers, and hence a layered cyclic porousgeometry, which is usually considered to be unstable, can be constitutedstably with superior mechanical strength.

[0024] Preferably, the invention is characterized in that the inorganicdielectric film is formed by repeatedly laminating, on and in parallelwith the surface of the substrate, a first porous structure domain layerin which columnar pores are arranged cyclically, and a second porousstructure domain in which layered pores are cyclically arranged inparallel with the surface of the substrate.

[0025] In addition to yielding the previously-described effects, theconfiguration enables the pores to assume a closed structure having noopening sections for upper layer and lower layer wiring, particularlywhen the dielectric film is used as an interlayer dielectric film.Hence, the dielectric film plays the role of a low dielectric thin filmhaving superior moisture resistance and higher reliability.

[0026] Preferably, the invention is further characterized in that theinorganic dielectric film comprises a semiconductor substrate, or afirst layer wiring conductor formed on the surface of the semiconductorsubstrate, and an interlayer dielectric film interposed between thesemiconductor substrate or the first layer wiring conductor, and asecond layer wiring conductor formed thereon.

[0027] Such a configuration enables formation of a dielectric film oflow capacitance. Hence, parasitic capacitance can be reduced, and thesemiconductor device can be made faster.

[0028] Preferably, the invention is characterized by comprising a firstinterlayer dielectric film region which is formed on the first layerwiring conductor and has contact holes to contact the first layer wiringconductor, and a second interlayer dielectric film to be charged into aninter-wiring area of a second layer wiring conductor formed on the firstinterlayer dielectric film, wherein the first interlayer dielectric filmis formed from a second porous structure domain in which layered poresare arranged cyclically.

[0029] According to this configuration, the second porous structuredomain in which the layered pores are arranged cyclically is constitutedin the area surrounding the contact hole. Hence, interlayer capacitancecan be reduced.

[0030] More preferably, the invention is further characterized in thatthe interlayer dielectric film comprises a first interlayer dielectricfilm region which is formed on the first layer wiring conductor and hascontact holes to contact the first layer wiring conductor, and a secondinterlayer dielectric film to be charged into an inter-wiring area of asecond layer wiring conductor formed on the first interlayer dielectricfilm, wherein the first interlayer dielectric film is formed from asecond porous structure domain in which layered pores are arrangedcyclically, and the second interlayer dielectric film is formed from afirst porous structure domain in which columnar pores are arrangedcyclically.

[0031] According to this configuration, the second porous structuredomain in which the layered pores are arranged cyclically is constitutedin the area surrounding the contact hole. Hence, interlayer capacitancecan be reduced. Columnar pores are arranged laterally in an upper layerwiring area constituting an inter-wiring dielectric film. For thisreason, lateral capacitance is diminished to a great extent. Preferably,use of a first porous structure domain arranged such that the directionin which the columnar pores are arranged becomes parallel with a wiringdirection enables provision of a highly reliable semiconductor devicewithout involvement of occurrence of a problem of short circuit betweenwiring lines.

[0032] Preferably, the invention is further characterized in that theinterlayer dielectric film comprises a first interlayer dielectric filmwhich is formed on the first layer wiring conductor and has contactholes to contact the first layer wiring conductor, and a secondinterlayer dielectric film to be charged into an inter-wiring area of asecond layer wiring conductor formed on the first interlayer dielectricfilm, wherein the first interlayer dielectric film is formed from asecond porous structure domain in which layered pores formed so as tobecome parallel with the surface of the substrate are arrangedcyclically, and the second interlayer dielectric film is formed from athird porous structure domain in which layered pores formed so as tobecome substantially perpendicular to the surface of the substrate arearranged cyclically.

[0033] According to this configuration, the second porous structuredomain in which the layered pores are arranged cyclically so as tobecome parallel with the surface of the substrate is constituted in thearea surrounding the contact hole. Hence, interlayer capacitance can bereduced. In the upper layer wiring area constituting the interlayerdielectric film, layered pores are arranged cyclically so as to becomesubstantially perpendicular to the surface of the substrate. Hence,lateral capacitance is diminished further, and there can be provided ahighly reliable semiconductor device which does not involve occurrenceof a problem of a short circuit between wiring lines.

[0034] A method for manufacturing a semiconductor device according tothe invention is characterized in that processes for forming aninterlayer dielectric film comprise a process of producing a firstprecursor solution containing a silica derivative and a surface activeagent so as to assume a first composition ratio at which pores arearranged cyclically; a process of producing a second precursor solutioncontaining a silica derivative and a surface active agent so as toassume a second composition ratio at which pores are arrangedcyclically; a preliminary crosslinking process which raises thetemperature of the first precursor solution and that of the secondprecursor solution, to thus initiate a crosslinking reaction; a contactprocess for bringing into contact with the surface of the substrate thefirst and second precursor solutions that have started the cross linkingreaction in the preliminary crosslinking process; and a process forsintering the substrate with which the first and second precursorsolutions have been brought into contact, so as to decompose and removethe surface active agent, whereby a dielectric film is formed.

[0035] By means of such a configuration, there can be provided adielectric film which has extremely superior controllability, superiormechanical strength, and a minimum dielectric constant. Further, therecan be readily formed an interlayer dielectric film having cyclicstructures of two types or more, such as an interlayer dielectric filmformed from a first porous structure domain layer in which columnarpores are arranged cyclically and a second porous structure domain layerin which layered pores are cyclically arranged in parallel with thesurface of the substrate, both being repeatedly stacked on and inparallel with the surface of the substrate.

[0036] Since the dielectric film can be formed at low temperature, ahighly reliable dielectric film can be formed without affecting thesubstrate, even when the dielectric film is used as an interlayerdielectric film of an integrated circuit. Since the dielectric film canbe formed without involvement of a heating process of 500° C. or more,the invention can also be applied to a case where aluminum wiring isemployed.

[0037] Since the dielectric film can be formed by means of contact ofliquid, a pattern can be formed with high accuracy within a minute area,thereby improving reliability.

[0038] A pore ratio can be changed appropriately by adjusting theconcentration of a precursor solution. A dielectric thin film of desireddielectric constant can be formed with extremely superior operability.

[0039] The method of the invention is further characterized in that apreliminary crosslinking reaction is initiated after the first andsecond precursor solutions having been brought into contact with thesurface of the substrate.

[0040] The method enables easy, efficient formation of an inorganicdielectric film in which pores having two or more types of periodicityare formed.

[0041] Preferably, the invention is characterized in that the contactprocess is a process for sequentially and repeatedly immersing thesubstrate into the first and second precursor solutions.

[0042] The configuration enables formation, with superior productivity,of a low dielectric thin film in which different porous structuredomains are stacked.

[0043] Preferably, the invention is characterized in that the contactprocess includes a process for immersing the substrate into the firstprecursor solution and raising the substrate at a desired speed, and aprocess for immersing the substrate into the second precursor solutionand raising the substrate at a desired speed.

[0044] Preferably, the invention is characterized in that the contactprocess is a process for sequentially and repeatedly applying the firstand second precursor solutions over the substrate.

[0045] More preferably, the invention is characterized in that thecontact process is a spin coating process for dropping the first andsecond precursor solutions on the substrate and spinning the substrate.

[0046] Such a configuration enables easy adjustment of a film thicknessor a pore ratio. A low dielectric thin film can be formed with superiorproductivity.

[0047] Preferably, the invention is characterized in that the inorganicdielectric film is formed on the surface of the substrate and has acyclic porous structure including columnar pores oriented so as tobecome parallel with the surface of the substrate and having a poreratio of 50% or higher.

[0048] According to such a configuration, the pores are oriented inparallel with the surface of the substrate. Hence, a low, uniformdielectric constant is achieved in the direction perpendicular to thesurface of the substrate. Particularly when the dielectric film is usedas an interlayer dielectric film, the pores can assume a closedstructure in which no opening sections are provided for upper layerwiring or lower layer wiring. Hence, the dielectric film plays the roleof an effective low dielectric thin film having superior moistureresistance and enhanced reliability.

[0049] Preferably, the invention is characterized in that the inorganicdielectric film is formed on the surface of the substrate and includes aplurality of cyclic porous structure domains containing columnar poresoriented in one direction so as to become parallel with the surface ofthe substrate; and adjacent porous structure domains are oriented indifferent directions.

[0050] Moreover, the porous structure is oriented in a differentdirection in each domain. Hence, the opening sections of the pores canbe closed by each other. There can be obtained a low dielectric thinfilm having superior moisture resistance substantially equal to that ofa dense film, superior mechanical strength derived from a cyclicstructure, and an ultimately low dielectric constant. An interlayerspace is supported by adjacent layers, and hence a layered cyclic porousgeometry, which is usually considered to be unstable, can be constitutedstably with superior mechanical strength.

[0051] Preferably, the invention is characterized in that the inorganicdielectric film is formed on the surface of the substrate and has acyclic porous structure domain in which layered pores are orientedcyclically in one direction so as to become parallel with the surface ofthe substrate.

[0052] According to such a configuration, the layered pores are orientedin parallel with the surface of the substrate. Hence, a low, uniformdielectric constant is achieved in the direction perpendicular to thesurface of the substrate. Particularly when the dielectric film is usedas an interlayer dielectric film, the pores can assume a closedstructure in which no opening sections are provided for upper layerwiring or lower layer wiring. Hence, the dielectric film plays the roleof an effective low dielectric thin film having superior moistureresistance and enhanced reliability. Such a structure enables an attemptto realize a dielectric film which is higher in pore ratio and lower-indielectric constant than a dielectric film having columnar pores.

[0053] A method for manufacturing a semiconductor device according tothe invention is characterized by comprising: a process of producing aprecursor solution containing a silica derivative and a surface activeagent; a preliminary crosslinking process for commencing a crosslinkingreaction by increasing the temperature of the precursor solution; acontact process for bringing, into contact with the surface of thesubstrate, the precursor solution that has commenced the crosslinkingreaction in the preliminary crosslinking process; and a process forsintering the substrate with which the precursor solution has beenbrought into contact to decompose and remove the surface active agent.

[0054] According to such a configuration, there can be provided adielectric film which has extremely superior controllability, superiormechanical strength, and a minimum dielectric constant. Since thedielectric film can be formed at low temperature, a highly-reliabledielectric film can be formed without affecting the substrate even whenthe dielectric film is used as an interlayer dielectric film of anintegrated circuit.

[0055] The pore rate can be adjusted as required by adjusting theconcentration of the precursor solution. A dielectric thin film ofdesired dielectric constant can be formed with extremely superioroperability.

[0056] Preferably, the invention is characterized in that the contactprocess is a process for immersing the substrate into the precursorsolution.

[0057] The configuration enables formation of a low dielectric thin filmwith superior productivity.

[0058] Preferably, the invention is characterized in that the contactprocess includes a process for immersing the substrate into theprecursor solution and raising the substrate at a desired speed.

[0059] The configuration enables formation of a low dielectric thin filmwith superior productivity.

[0060] Preferably, the invention is characterized in that the contactprocess is a process for applying the precursor solution over thesubstrate.

[0061] The configuration enables formation of a low dielectric thin filmwith superior productivity.

[0062] Preferably, the invention is characterized in that the contactprocess is a spin coating process for dropping the precursor solution onthe substrate and spinning the substrate.

[0063] The configuration enables easy adjustment of a film thickness ora pore ratio and formation of a low dielectric thin film with superiorproductivity.

[0064] The invention is characterized by further comprising an inorganicdielectric film which is formed on the surface of the substrate and hasa porous structure whose framework surrounds pores and is coated with ahydrophobic layer.

[0065] By means of such a configuration, exterior and interior surfacesof a framework surrounding pores of the porous structure are reformedwith a hydrophobic layer on a molecular level, thereby enhancingmoisture resistance while the mechanical strength of the film ismaintained. Since the dielectric constant of air is low, by means of theporous structure the dielectric constant of the dielectric film can bereduced further as compared with the case where the dielectric film isdoped with fluorine. Hence, the dielectric constant of the dielectricfilm can be minimized.

[0066] Preferably, the invention is characterized in that the inorganicdielectric film is formed on the surface of the substrate, and the poreshave an orientation characteristic.

[0067] According to the configuration, the pores possess the orientationcharacteristic and a cyclic porous structure. Hence, mechanical strengthof the dielectric film can be enhanced, and a dielectric film havinghigh reliability can be obtained.

[0068] Preferably, the invention is characterized in that the inorganicdielectric film is formed on the surface of the substrate and has acyclic porous structure in which columnar pores are oriented so as tobecome parallel with the surface of the substrate.

[0069] According to such a configuration, the pores are oriented inparallel with the surface of the substrate. Hence, a low, uniformdielectric constant is achieved in the direction perpendicular to thesurface of the substrate. Particularly when the dielectric film is usedas an interlayer dielectric film, the pores can assume a closedstructure in which no opening sections are provided for upper layerwiring or lower layer wiring. Hence, the dielectric film plays the roleof an effective low dielectric thin film having superior moistureresistance and enhanced reliability.

[0070] Preferably, the invention is characterized in that the inorganicdielectric film is formed on the surface of the substrate and includes aplurality of cyclic porous structure domains containing columnar poresoriented in one direction so as to become parallel with the surface ofthe substrate; and adjacent porous structure domains are oriented indifferent directions.

[0071] According to the configuration, the porous structure is orientedin a different direction in each domain. Hence, the opening sections ofthe pores can be closed by each other. There can be obtained a lowdielectric thin film having superior moisture resistance substantiallyequal to that of a dense film, superior mechanical strength derived froma cyclic structure, and an ultimately low dielectric constant. Aninterlayer space is supported by adjacent layers, and hence a layeredcyclic porous geometry, which is usually considered to be unstable, canbe constituted stably with superior mechanical strength.

[0072] Preferably, the invention is characterized in that the inorganicdielectric film has a cyclic porous structure including layered pores.

[0073] In addition to yielding the foregoing effects, the configurationenables an attempt to increase the pore ratio and to lower thedielectric constant further.

[0074] Preferably, the invention is characterized in that the inorganicdielectric film has a cyclic porous structure including layered poresoriented so as to become parallel with the surface of the substrate.

[0075] Preferably, the invention is characterized in that the inorganicdielectric film has a cyclic porous structure domain including layeredpores possessing two or more types of spatial orientationcharacteristics.

[0076] According to such a configuration, there can be provided aninorganic dielectric film having uniform, high mechanical strength and alow dielectric constant. In addition to yielding the foregoing effects,the configuration enables the pores to assume a closed structure inwhich no opening sections are provided for upper layer wiring or lowerlayer wiring particularly when the dielectric film is used as aninterlayer dielectric film. Hence, the dielectric film plays the role ofan effective low dielectric thin film having superior moistureresistance and enhanced reliability.

[0077] More preferably, the invention is characterized in that theinorganic dielectric film is formed by means alternately stacking acyclic porous structure including layered pores and a cyclic porousstructure including columnar pores so as to become parallel with thesurface of the substrate.

[0078] Preferably, the invention is characterized in that the inorganicdielectric film is formed by alternately stacking a first layer having acyclic porous structure domain including layered pores of two or moretypes of orientation characteristics, and a second layer having a cyclicporous structure domain including columnar pores having two or moretypes of orientation characteristics, so as to become parallel with thesurface of the substrate.

[0079] Preferably, the invention is characterized in that the inorganicdielectric film has a porous structure having pores constituting athree-dimensional network.

[0080] According to the structure, the pores constitute thethree-dimensional network. Hence, the paths of the pores become longer,and closing of the opening sections of the pores by each other in alinear direction becomes easy. There can be obtained a low dielectricthin film having superior moisture resistance substantially equal tothat of a dense film, superior mechanical strength, and an ultimatelylow dielectric constant.

[0081] Preferably, the invention is characterized in that the inorganicdielectric film is a semiconductor substrate or a lower layer wiringconductor formed thereon, and an interlayer dielectric film isinterposed between the semiconductor substrate or the lower layer wiringconductor, and an upper layer wiring conductor.

[0082] The configuration enables an attempt to diminish a dielectricconstant of the interlayer dielectric film. Hence, a decrease ininterlayer capacitance and provision of a semiconductor device whichoperates at high speed can be realized.

[0083] A second invention is characterized by providing a method formanufacturing a semiconductor device, comprising: a process of producinga precursor solution containing a silica derivative and a surface activeagent; a contact process for bringing the precursor solution that hascommenced the crosslinking reaction in the preliminary crosslinkingprocess into contact with the surface of the substrate; a process forsintering the substrate with which the precursor solution has beenbrought into contact, to thereby decompose and remove the surface activeagent; and a process for subjecting a silica thin film of porousstructure obtained in the decomposition removal process to hydrophobictreatment, thereby forming a dielectric film of porous structure havinga framework whose surface is coated with a hydrophobic layer.

[0084] The configuration enables provision of a dielectric film whichhas extremely high controllability, high moisture resistance, superiormechanical strength, and an extremely low dielectric constant. Since thedielectric film can be formed at low temperature, a highly reliabledielectric film can be formed without affecting the substrate, even whenthe dielectric film is used as an interlayer dielectric film of anintegrated circuit. Finally, the moisture resistance can be enhanced bymerely subjecting the dielectric film to hydrophobic treatment, and thusthe reliability of the dielectric film can be improved very easily.

[0085] Preferably, the invention further comprises a preliminarycrosslinking process, preceding the contact process, for raising thetemperature of the precursor solution in order to initiate acrosslinking reaction.

[0086] Such a configuration enables a further improvement inproductivity.

[0087] The pore rate can be adjusted as required by adjusting theconcentration of the precursor solution. A dielectric thin film ofdesired dielectric constant can be formed with extremely superioroperability.

[0088] Preferably, the invention is characterized in that thehydrophobic treatment process is a sililation process.

[0089] The configuration enables easy formation of a hydrophobic layerby merely exposing the dielectric film to a sililation solution, mist,or vapor.

[0090] Preferably, the invention is characterized in that the contactprocess is a process for immersing the substrate into the precursorsolution.

[0091] The configuration enables formation of a low dielectric thin filmwith superior productivity.

[0092] Preferably, the invention is characterized in that the contactprocess is a process for immersing the substrate into the precursorsolution and raising the substrate at a desired speed.

[0093] The configuration enables formation of a low dielectric thin filmwith superior productivity.

[0094] Preferably, the invention is characterized in that the contactprocess is a process for applying the precursor solution over thesubstrate.

[0095] The configuration enables formation of a low dielectric thin filmwith superior productivity.

[0096] Preferably, the invention is characterized in that the contactprocess is a spin coating process for dropping the precursor solution onthe substrate and spinning the substrate.

[0097] The configuration enables easy adjustment of a film thickness ora pore ratio and formation of a low dielectric thin film with superiorproductivity.

[0098] The invention is characterized by further comprising an inorganicdielectric film which is formed on the surface of the substrate and hasa porous structure having pores which constitute a three-dimensionalnetwork.

[0099] Since the dielectric constant of air is low, by means of such aconfiguration the low dielectric film can be reduced further as comparedwith the case where the dielectric film is doped with fluorine. Hence,the dielectric constant of the dielectric film can be minimized. Thepores constitute a three-dimensional network, and hence the physicalproperties of the film can be rendered uniform. Further, the resultantelectrical characteristic is isotropic. The paths of the pores becomelonger, and closing of the opening sections of the pores by each otherin a linear direction becomes easy. There can be obtained a lowdielectric thin film having superior moisture resistance substantiallyequal to that of a dense film, superior mechanical strength, and anultimately low dielectric constant.

[0100] Preferably, the invention is characterized by further comprisinga porous structure having pores constituting a three-dimensional cyclicnetwork.

[0101] According to the configuration, the pores assume a porousstructure having pores which constitute a cyclic three-dimensionalnetwork. Hence, the mechanical strength of the film can be enhanced, anda highly reliable dielectric film can be obtained.

[0102] Preferably, the invention is characterized in that the inorganicdielectric film is a semiconductor substrate or a lower layer wiringconductor formed thereon, and an interlayer dielectric film isinterposed between the semiconductor substrate or the lower layer wiringconductor, and an upper layer wiring conductor.

[0103] The configuration enables an attempt to lowers a dielectricconstant of the interlayer dielectric film. Hence, a decrease ininterlayer capacitance and provision of a semiconductor device whichoperates at high speed can be realized.

[0104] The invention is characterized by providing a method formanufacturing a semiconductor device, comprising: a process of producinga precursor solution containing a silica derivative and a surface activeagent; a contact process for bringing the precursor solution intocontact with the surface of a substrate; and a process for sintering thesubstrate with which the precursor solution has been brought intocontact, to thereby decompose and remove the surface active agent.

[0105] The configuration enables provision of a dielectric film whichhas extremely high controllability, superior mechanical strength, and anextremely low dielectric constant. Since the dielectric film can beformed at low temperature, a highly reliable dielectric film can beformed without affecting the substrate even when the dielectric film isused as an interlayer dielectric film of an integrated circuit.

[0106] Preferably, the invention further comprises a preliminarycrosslinking process, preceding the contact process, for raising thetemperature of the precursor solution in order to initiate acrosslinking reaction.

[0107] Such a configuration enables a further improvement inproductivity.

[0108] The pore ratio can be adjusted as required by adjusting theconcentration of the precursor solution. A dielectric thin film ofdesired dielectric constant can be formed with extremely superioroperability.

[0109] Preferably, the invention is characterized in that the contactprocess is a process for immersing the substrate into the precursorsolution.

[0110] The configuration enables formation of a low dielectric thin filmwith superior productivity.

[0111] Preferably, the invention is characterized in that the contactprocess is a process for immersing the substrate into the precursorsolution and raising the substrate at a desired speed.

[0112] The configuration enables formation of a low dielectric thin filmwith superior productivity.

[0113] Preferably, the invention is characterized in that the contactprocess is a process for applying the precursor solution over thesubstrate.

[0114] The configuration enables formation of a low dielectric thin filmwith superior productivity.

[0115] Preferably, the invention is characterized in that the contactprocess is a spin coating process for dropping the precursor solution onthe substrate and spinning the substrate.

[0116] The configuration enables easy adjustment of a film thickness ora pore ratio and formation of a low dielectric thin film with superiorproductivity.

[0117] The invention is also characterized by further comprising aninorganic dielectric film which is formed on the surface of thesubstrate and which has a porous structure containing at least onesupport member in the pore.

[0118] According to the configuration, a columnar structure of molecularsize is contained in the pore section of the cyclic porous structure,whereby the resistance of the pore section to external force can beincreased. Since the dielectric constant of air is low, by means of sucha configuration the dielectric constant of the dielectric film can belowered further as compared with the case where the dielectric film isdoped with fluorine. Hence, the dielectric constant of the dielectricfilm can be minimized. Preferably, the pore ratio is set to a value of50% or higher. Thus, the columnar members are inserted into pores,thereby constituting support members. As a result, the mechanicalstrength of the film is enhanced to a great extent, and a porousstructure having an extremely high pore ratio can be obtained.

[0119] Preferably, the invention is characterized in that the inorganicdielectric film is formed on the surface of the substrate, and the porespossess the orientation characteristic.

[0120] In addition to yielding the foregoing effects, the configurationenables an increase in mechanical strength of the dielectric film,because the pores possess the orientation characteristic and theinorganic dielectric film has the cyclic porous structure. There can beformed a highly-reliable dielectric film.

[0121] Preferably, the invention is characterized in that the inorganicdielectric film is formed on the surface of the substrate and hascolumnar pores and a cyclic porous structure including support membersarranged within the columnar pores so as to extend across the diameterof a bottom surface thereof.

[0122] According to the configuration, the support member serving as asupport is inserted into the columnar pore so as to extend across thediameter of the bottom surface. Hence, the mechanical strength of thefilm can be increased to a great extent. Further, the pores areoriented, and hence the pore ratio can be improved, and there can beformed an effective low dielectric thin film having superior mechanicalstrength and high reliability.

[0123] Preferably, the invention is characterized in that the inorganicdielectric film is formed on the surface of the substrate and hascolumnar pores oriented so as to become parallel with the surface of thesubstrate, as well as a cyclic porous structure including supportmembers arranged within the columnar pore so as to extend across thediameter of a bottom surface thereof.

[0124] According to the configuration, the support member serving as asupport is inserted into the columnar pore so as to extend across thediameter of the bottom surface. Hence, the mechanical strength of thefilm can be increased to a great extent. Since the pores are oriented soas to become parallel with the surface of the substrate, a low, uniformdielectric constant is achieved in the direction perpendicular to thesurface of the substrate. Particularly when the dielectric film is usedas an interlayer dielectric film, the pores can assume a closedstructure in which no opening sections are provided for upper layerwiring or lower layer wiring. Hence, the dielectric film plays the roleof an effective low dielectric thin film having superior moistureresistance and enhanced reliability.

[0125] Preferably, the invention is characterized in that the inorganicdielectric film is formed on the surface of the substrate and includes aplurality of cyclic porous structure domains containing columnar poresoriented in one direction so as to become parallel with the surface ofthe substrate; and adjacent porous structure domains are oriented indifferent directions.

[0126] In addition to yielding the effect of increasing mechanicalstrength of the film, the configuration enables the opening sections ofthe pores to close each other, because the porous structure is orientedin a different direction in each domain. Hence, there can be obtained alow dielectric thin film having superior moisture resistancesubstantially equal to that of a dense film, superior mechanicalstrength derived from a cyclic structure, and an ultimately lowdielectric constant.

[0127] Preferably, the invention is characterized in that the inorganicdielectric film is formed on the surface of the substrate and haslayered pores and a cyclic porous structure including support membersarranged in the layered pores so as to support an interlayer space.

[0128] Further, an interlayer space is supported by adjacent layers, andhence a layered cyclic porous geometry, which is usually considered tobe unstable, can be constituted stably with superior mechanicalstrength. Particularly, the invention solves a problem of a dielectricfilm having a layered cyclic porous structure from among cyclic porousstructures having a very high pore ratio but being thermally unstableand usually difficult to form. However, according to the configuration,a columnar structure of molecular size is included in the pore sectionof the layered cyclic porous structure, thereby enhancing thermalstability of the film and increasing the mechanical strength of the filmto a great extent.

[0129] Preferably, the invention is characterized in that the inorganicdielectric film is formed on the surface of the substrate and includes aplurality of cyclic porous structure domains containing layered poresoriented so as to become parallel with the surface of the substrate; andadjacent porous structure domains are oriented in different directions.

[0130] According to the configuration, the porous structure domains areoriented on the molecular scale. However, the film is apparently madeuniform on the scale of wiring. Various physical film properties,including electrical characteristics such as a relative dielectricconstant, do not possess any anisotropy, and the film is uniform,thereby enabling practical use of the film. Particularly when thedielectric film is used as an interlayer dielectric film, the pores canassume a closed structure in which no opening sections are provided forupper layer wiring or lower layer wiring. Hence, the dielectric filmplays the role of an effective low dielectric thin film having superiormoisture resistance and enhanced reliability.

[0131] Preferably, the invention is characterized in that the inorganicdielectric film is a semiconductor substrate or a lower layer wiringconductor formed thereon, and an interlayer dielectric film isinterposed between the semiconductor substrate or the lower layer wiringconductor, and an upper layer wiring conductor.

[0132] The configuration enables an attempt to lowers a dielectricconstant of the interlayer dielectric film. Hence, a decrease ininterlayer capacitance and provision of a semiconductor device whichoperates at high speed can be realized.

[0133] A method for manufacturing a semiconductor device according tothe invention is characterized by comprising: a process of producing aprecursor solution containing a silica derivative and a surface activeagent; a contact process for bringing the precursor solution intocontact with the surface of the substrate; a substitution process forreplacing, through substitution, at least a portion of the surfaceactive agent of the precursor solution with a compound constituting asupport member of molecular size; and a process for sintering thesubstrate to decompose and remove the surface active agent, whereby adielectric film is formed.

[0134] A method for manufacturing a semiconductor device according tothe invention is characterized by comprising: a process of producing aprecursor solution containing a silica derivative and a surface activeagent; a preliminary crosslinking process which raises the temperatureof the precursor solution, to thus initiate a crosslinking reaction; acontact process for bringing the precursor solution that has started thecrosslinking reaction in the preliminary crosslinking process intocontact with the surface of the substrate; a substitution process forreplacing, through substitution, at least a portion of the surfaceactive agent of the precursor solution with a compound constituting asupport member of molecular size; and a process for sintering thesubstrate to decompose and remove the surface active agent.

[0135] According to the configuration, by means of inclusion of only asubstitution process there can be provided a dielectric film which hasextremely superior controllability, superior mechanical strength, and anultimately low dielectric constant. Since the dielectric film can beformed at low temperature, a highly reliable dielectric film can beformed without affecting the substrate even when the dielectric film isused as an interlayer dielectric film of an integrated circuit.

[0136] Further, the pore ratio can be adjusted as required by adjustingthe concentration of the precursor solution. A dielectric thin film ofdesired dielectric constant can be formed with extremely superioroperability.

[0137] Preferably, the invention is characterized in that thesubstitution process is a process for replacing at least a portion ofthe surface active agent with an organic molecule.

[0138] Substitution employing organic molecules facilitates selection ofmolecules matching the pores, thereby enabling an attempt to easilyincrease mechanical strength.

[0139] Preferably, the invention is characterized in that thesubstitution process is a process for replacing at least a portion ofthe surface active agent with an inorganic molecule.

[0140] The configuration yields an effect of improving heat resistance.

[0141] Namely, in a case where the surface active agent is formed fromcations, the surface active agent is subjected to ion exchange throughuse of a cationic inorganic compound. In contrast, in a case where thesurface active agent is formed from anions, the surface active agent issubjected to ion exchange through use of an anionic inorganic compound.In a case where the surface active agent is neutral, the surface activeagent is replaced with a neutral inorganic compound. In an ion exchangeprocess, inorganic ions which exhibit interaction greater than thatdeveloping between ions of the surface active agent and the silicaserving as a base material until exchange are used between the silicaserving as the base material and the inorganic compound. As a result,ion exchange can be induced more efficiently.

[0142] Even when the surface active agent and the inorganic compound areexchanged with each other without involvement of ion exchange, exchangecan be induced more efficiently, depending on the magnitude ofinteraction developing between the silica serving as the base materialand the inorganic compound.

[0143] Further, a reaction which develops between surface active agentmolecules and inorganic ions can also be replaced with a neutralinorganic compound. In this case, exchanging reaction is induced whileelectric charges are maintained by concurrent use of an acid or base,thereby enabling efficient exchange.

[0144] Preferably, the invention is characterized in that thesubstitution process is a process for replacing at least a portion ofthe surface active agent with an inorganic molecule.

[0145] Preferably, the invention is characterized in that thesubstitution process is a process for replacing the surface active agentwith superfine particles of an inorganic compound.

[0146] When cetyltrimethyl ammonium bromide [CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] isemployed as a surface active agent, an interval between layers beforethe substrate is subjected to sintering corresponds to two surfaceactive agent molecules; that is, a distance of 2.5 nm or thereabouts.For this reason, an inorganic compound molecule of substantially equalsize can be caused to approach the surface active agent molecule byutilization of a diffusion phenomenon attributable to a concentrationgradient, to thereby enable replacement through ion exchange.

[0147] An inorganic compound molecule equal in size with the intervalbetween the layers maybe caused to approach the surface active agentmolecule by utilization of the diffusion phenomenon attributable to aconcentration gradient. An exchange phenomenon stemming from formationof a new link may also be utilized.

[0148] In relation to such a substitutional molecule, one molecule maycorrespond to the interval between the layers. However, an aggregateformed from a plurality of molecules, such as four or five molecules,may be used so as to correspond to a single interval between the layers.

[0149] When the diameter of the molecule is greater than the intervalbetween the layers, substitution is effected such that the interval ismade larger through exchange.

[0150] When the diameter of the molecule is almost equal to the intervalbetween the layers, substitution is effected such that the intervalremains substantially constant through exchange.

[0151] When the diameter of the molecule is smaller than the intervalbetween the layers, substitution is effected such that the intervalbecomes smaller through exchange.

[0152] Preferably, the invention is characterized in that the inorganiccompound is hydrated magnesia (MgO)_(m)(H₂O)_(n).

[0153] The magnesia molecules (MgO)_(m)(H₂O)_(n) remain hydrated in asolution. Surfaces of the particles are charged positive δ+, and δ−oxygen atoms of H₂O or OH are coordinated with the surfaces. Themagnesia molecules may be formed from linear or oval MgO superfineparticles or a cluster which constitutes an agglomerate of molecules.Preferably, the molecules assume a diameter of 10 nm or less, morepreferably a diameter of 4 nm or less.

[0154] Preferably, the invention is characterized in that thesubstitution process includes a process for growing the inorganiccompound molecules in the pores through diffusion.

[0155] Preferably, the invention is characterized in that thesubstitution process includes a process for replacing, throughsubstitution, a single or a plurality of straight chain silanolmolecules produced from hydrolysis polycondensation reaction ofsilicon-hydroxide-based molecules.

[0156] Preferably, the invention is characterized in that the contactprocess is a process for immersing the substrate into the precursorsolution.

[0157] The configuration enables formation of a low dielectric thin filmwith superior productivity.

[0158] Preferably, the invention is characterized in that the contactprocess is a process for immersing the substrate into the precursorsolution and raising the substrate at a desired speed.

[0159] The configuration enables formation of a low dielectric thin filmwith superior productivity.

[0160] Preferably, the invention is characterized in that the contactprocess is a process for applying the precursor solution over thesubstrate.

[0161] The configuration enables formation of a low dielectric thin filmwith superior productivity.

[0162] Preferably, the invention is characterized in that the contactprocess is a spin coating process for dropping the precursor solution onthe substrate and spinning the substrate. The configuration enables easyadjustment of a film thickness or a pore ratio and formation of a lowdielectric thin film with superior productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0163]FIG. 1 is a view showing a semiconductor device of multilayerwiring structure using a dielectric film formed by means of a methodaccording to a first embodiment of the invention;

[0164]FIG. 2 is a view showing processes for manufacturing thesemiconductor device of multilayer wiring structure shown in FIG. 1;

[0165]FIG. 3 is a descriptive view showing processes for forming thedielectric film of the first embodiment of the invention;

[0166]FIG. 4 is a descriptive view showing an interlayer dielectric filmof the first embodiment of the invention;

[0167]FIG. 5 is a structural descriptive view showing the interlayerdielectric film of the first embodiment of the invention;

[0168]FIG. 6 is a descriptive view showing a semiconductor deviceaccording to a second embodiment of the invention;

[0169]FIG. 7 is a view showing FRAM using a dielectric film formed bymeans of a method according to a third embodiment of the invention;

[0170]FIG. 8 is a view showing processes for manufacturing the FRAMshown in FIG. 7;

[0171]FIG. 9 is a descriptive view showing processes for forming thedielectric film of the third embodiment of the invention;

[0172]FIG. 10 is a descriptive view showing a method for forming adielectric film according to a fourth embodiment of the invention;

[0173]FIG. 11 is a view showing FRAM using the dielectric film formed bymeans of a method according to a fifth embodiment of the invention;

[0174]FIG. 12 is a descriptive view showing a dielectric film accordingto a sixth embodiment of the invention;

[0175]FIG. 13 is a view showing a semiconductor device of multilayerwiring structure using a dielectric film formed by means of a methodaccording to a seventh embodiment of the invention;

[0176]FIG. 14 is a view showing processes for manufacturing thesemiconductor device of multilayer wiring structure shown in FIG. 13;

[0177]FIG. 15 is a view showing an interlayer dielectric film accordingto a seventh embodiment of the invention;

[0178]FIG. 16 is a structural descriptive view showing the interlayerdielectric film according to the seventh embodiment of the invention;

[0179]FIG. 17 is a descriptive view showing a semiconductor deviceaccording to an eighth embodiment of the invention;

[0180]FIG. 18 is a view showing FRAM using a dielectric film formed bymeans of a method according to a ninth embodiment of the invention;

[0181]FIG. 19 is a view showing FRAM using a dielectric film formed bymeans of a method according to an eleventh embodiment of the invention;

[0182]FIG. 20 is a structural descriptive view of a dielectric filmaccording to a fourteenth embodiment of the invention;

[0183]FIG. 21 is a view showing a semiconductor device of multilayerwiring structure using the dielectric film formed by means of the methodof the fourteenth embodiment of the invention;

[0184]FIG. 22 is a view showing processes of manufacturing thesemiconductor device of multilayer wiring structure shown in FIG. 20;

[0185]FIG. 23 is a descriptive view showing the interlayer dielectricfilm of the fourteenth embodiment of the invention;

[0186]FIG. 24 is a structural descriptive view showing the interlayerdielectric film of the fourteenth embodiment of the invention;

[0187]FIG. 25 is a structural descriptive view showing the interlayerdielectric film of the fourteenth embodiment of the invention;

[0188]FIG. 26 is a view showing FRAM using a dielectric film formed bymeans of a method according to a fifteenth embodiment of the invention;

[0189]FIG. 27 is a structural descriptive view showing a modification ofa dielectric film of low dielectric constant according to the invention;

[0190]FIG. 28 is a structural descriptive view showing a modification ofthe dielectric film of low dielectric constant according to theinvention;

[0191]FIG. 29 is a structural descriptive view showing a modification ofthe dielectric film of low dielectric constant according to theinvention; and

[0192]FIG. 30 is a structural descriptive view showing a modification ofthe dielectric film of low dielectric constant according to theinvention.

[0193] In the drawings,

[0194]1S SILICON SUBSTRATE

[0195]12 FIRST WIRING LAYER

[0196]13 a FIRST INTERLAYER DIELECTRIC FILM

[0197]13 b SECOND INTERLAYER DIELECTRIC FILM

[0198]13S SECOND INTERLAYER DIELECTRIC FILM

[0199]14 SECOND WIRING LAYER

[0200] H CONTACT HOLE

[0201]1 SILICON SUBSTRATE

[0202]2 ELEMENT ISOLATION DIELECTRIC FILM

[0203]3 GATE DIELECTRIC FILM

[0204]4 GATE ELECTRODE

[0205]5 SOURCE REGION

[0206]6 DRAIN REGION

[0207]7 DIELECTRIC FILM

[0208]8 CONTACT HOLE

[0209]9 LOWER ELECTRODE

[0210]10 FERROELECTRIC FILM

[0211]11 UPPER ELECTRODE

BEST MODES FOR IMPLEMENTING THE INVENTION FIRST EMBODIMENT

[0212] A semiconductor device of multilayer wiring structure using a lowdielectric thin film as an interlayer dielectric film will be describedas a first embodiment of the invention.

[0213] As shown in FIG. 1, the semiconductor device is characterized inthat an interlayer dielectric film is formed from a dielectric filmhaving a two-layer structure and a low dielectric constant; that a firstinterlayer dielectric film 13 a having contact holes H to contact afirst wiring layer 12 is formed from a second porous structure domain inwhich layered pores are arranged cyclically so as to become parallelwith the surface of a substrate; and that a second interlayer dielectricfilm 13 b—which is formed on the first interlayer dielectric film 13 a,serves as an upper-layer portion, and is charged into inter-wiringregions of a second wiring layer 14—is formed from a first porousstructure domain in which columnar pores are arranged cyclically.

[0214] Specifically, a lower layer portion of the interlayer dielectricfilm—which is formed between the first wiring layer 12 formed on thesurface of an element region enclosed with an element isolationdielectric film (not shown) formed on the surface of a silicon substrate1S and the second wiring layer 14—is taken as a first interlayerdielectric film 13 a in which layered pores are arranged cyclically soas to become parallel with the surface of the substrate. The secondinterlayer dielectric film 13 b—which serves as an upper layer portionand is formed in a region between wiring patterns of the second wiringlayer 14 as an inter-line dielectric film—is formed from a first porousstructure domain in which columnar pores are arranged cyclically.

[0215] The other portions of the semiconductor device are of ordinarystructure, and their illustrations and explanations are omitted.

[0216] Processes of manufacturing the interlayer dielectric film willnow be described by reference to FIGS. 2A through 2D.

[0217] As shown in FIG. 2A, a desired semiconductor region is formed onthe surface of the silicon substrate 1S by means of an ordinary method,thereby forming a first wiring layer.

[0218] Subsequently, under the method of the invention, there is formeda mesoporous silica thin film in which the layered pores are arrangedcyclically so as to become parallel with the surface of the substrateand which is formed from a second cyclic porous structure domain (FIG.2B).

[0219] Specifically, as shown in FIG. 3A, cationic cetyltrimethylammonium bromide [CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] serving as a surface activeagent; tetramethoxy silane (TMOS) serving as a silica derivative; andhydrochloric acid (HCl) serving as an acid catalyst are dissolved intoan H₂O/alcohol mixed solvent, thereby preparing a precursor solutionwithin a mixing container. Mole ratios employed for preparing theprecursor solution are determined such that 0.5 parts surface activeagent, 5 parts silica derivative, and 2 parts acid catalyst are mixedtogether, with the solution being taken as 100 parts. The substratehaving the first wiring layer 12 formed thereon is immersed in themixture of solutions. As shown in FIG. 3B, after the mixing containerhas been sealed, the mixture is maintained at 30° C. to 150° C. for oneto 120 hours, whereby the silica derivative is subjected topolymerization through hydrolysis polycondensation reaction (apreliminary crosslinking process), thereby forming a cyclicself-agglomerate of the surface active agent.

[0220] As shown in FIG. 4A, the self-agglomerate forms a sphericalmicelle structure (FIG. 4B) into which a plurality of molecules, eachcomprising C₁₆H₃₃N⁺(CH₃)₃Br⁻, coagulate. There is formed a laminatedstructure (FIG. 4D) in which the surface active agent is oriented as thedegree of coagulation is increased as a result of an increase in density(FIG. 4C).

[0221] The substrate is raised and subjected to rinsing and drying.Subsequently, the substrate is heated and sintered for three hours in anoxygen atmosphere at 400° C., thereby completely removing the surfaceactive agent remaining in a mold through thermal decomposition. A puremesoporous silica thin film is formed.

[0222] As shown in FIG. 2B, thus is formed the first interlayerdielectric film 13 a in which the layered pores parallel with thesurface of the substrate are arranged. An enlarged descriptive view ofthe first interlayer dielectric film is shown in FIG. 4F. Here, aself-agglomerate of high density, such as that shown in FIG. 4D, isformed. An inorganic dielectric film in which layered pores are arrangedcan be formed by sintering the self-agglomerate.

[0223] As shown in FIG. 2C, through holes H are formed in the firstinterlayer dielectric film 13 a, and the second wiring layer 14 isformed by means of the ordinary method.

[0224] Subsequently, the second interlayer dielectric film 13 b isformed. The second interlayer dielectric film is formed in the samemanner as in the process for forming the first interlayer dielectricfilm 13 a. However, there is employed a precursor solution whosecomposition is changed from that of the precursor solution employed forforming the first interlayer dielectric film. Here, mole ratios employedfor preparing the precursor solution are determined such that 0.05 partssurface active agent, 0.1 parts silica derivative, and 2 parts acidcatalyst are mixed together with the solution being taken as 100 parts.In other respects, the second interlayer dielectric film is formed intotally the same manner as that employed for forming the firstinterlayer dielectric film.

[0225] As shown in FIG. 2D, there is obtained the second interlayerdielectric film 13 b formed from the first porous structure domain,wherein columnar pores are cyclically arranged.

[0226] Here, a spherical micelle structure into which a plurality ofmolecules, each comprising C₁₆H₃₃N⁺(CH₃)₃Br⁻, coagulate is furtherincreased in density, thereby forming a cylindrical substance in whichpores are oriented. Thus, a self-agglomerate such as that shown in FIG.4C is formed and sintered. Thus, there is obtained the second interlayerdielectric film 13 b formed from the first porous structure domain, suchas that shown in FIG. 4E, wherein columnar pores are cyclicallyarranged.

[0227]FIG. 5 is a structural descriptive view showing a cross section ofthe substrate in this state. As is evident from the drawing, themultilayer wiring structure is understood to comprise the firstinterlayer dielectric film 13 a formed from a porous thin film havingpores opened in the layered pattern, and the second interlayerdielectric film 13 b in which columnar pores are cyclically arranged.

[0228] In relation to the semiconductor device having the thus-formedmultilayer wiring structure, the interlayer dielectric film constitutes,in the region surrounding the contact holes H, the second porousstructure domain in which the layered pores are arranged cyclically.Hence, the interlayer capacitance can be diminished. Further, thecolumnar pores are arranged between wiring patterns within an upperlayer wiring region constituting an inter-wiring dielectric film, andhence inter-wiring capacitance is lowered. In the inter-wiringdielectric film serving as the upper-layer-side second interlayerdielectric film, the columnar pores are oriented so as to becomeparallel with the direction in which a wiring pattern of the secondwiring layer 14 is arranged. Hence, there can be provided asemiconductor device having high reliability without involvement of aproblem of occurrence of a short circuit between wiring patterns.

SECOND EMBODIMENT

[0229] In the first embodiment, the interlayer dielectric film is formedfrom a dielectric film having a two-layer structure and a low dielectricconstant. A lower layer portion of the interlayer dielectric film isformed from the second porous structure domain in which layered poresare arranged cyclically so as to become parallel with the surface of thesubstrate. An upper layer portion of the interlayer dielectric film isformed from the first porous structure domain in which the columnarpores are arranged cyclically. However, the upper layer portion of theinterlayer dielectric film may be formed from a third porous structuredomain which is perpendicular to the surface of the substrate and runsin parallel with a main wiring pattern, instead of the porous structuredomain having the columnar pores.

[0230] The structure of the third porous structure domain is shown inFIG. 6. As shown in FIG. 6, the semiconductor device is characterized inthat the interlayer dielectric film is formed from a dielectric filmhaving a two layer structure and a low dielectric constant; that thefirst interlayer dielectric film 13 a having the contact holes H thatcontact the first wiring layer 12 is formed from the second porousstructure domain in which layered pores are arranged cyclically so as tobecome parallel with the surface of the substrate; and that a secondinterlayer dielectric film 13S which is to be formed on the firstinterlayer dielectric film 13 a, serves as an upper layer portion, andis charged into an inter-wiring region of the second wiring layer 14 isformed from the third porous structure domain in which columnar poresare arranged cyclically.

[0231] Specifically, a lower layer portion of the interlayer dielectricfilm—which is formed between the first wiring layer 12 formed on thesurface of an element region enclosed with the element isolationdielectric film (not shown) formed on the surface of the siliconsubstrate 11 and the second wiring layer 14—is taken as the firstinterlayer dielectric film 13 a in which layered pores are arrangedcyclically so as to become parallel with the surface of the substrate.The second interlayer dielectric film 13S—which serves as an upper layerportion and is formed in a region between wiring patterns of the secondwiring layer as an inter-line dielectric film—is formed from the thirdporous structure domain which is perpendicular to the surface of thesubstrate and runs in parallel with the main wiring pattern.

[0232] The other portions of the semiconductor device are formed intotally the same manner as in the case of the first embodiment, andtheir illustrations and explanations are omitted.

[0233] By means of such a configuration, the inter-wiring capacitancecan be lowered further. Since the third porous structure domain runs inparallel with the main wiring pattern, a multilayer insulation wall ispresent between wiring patterns, whereby occurrence of a short circuitbetween wiring patterns can be prevented more reliably.

THIRD EMBODIMENT

[0234] FRAM using a low dielectric thin film as an interlayer dielectricfilm is described as a third embodiment of the invention.

[0235] As shown in FIG. 7A, the FRAM comprises a switching transistorfabricated in the element region enclosed with a element isolationdielectric film 2 formed on the surface of a silicon substrate 1, and aferroelectric capacitor. The invention is characterized by use of a thinfilm 7 of low dielectric constant of the invention as an interlayerdielectric film between the switching transistor and a lower electrode 9of the ferroelectric capacitor. As shown in an enlarged perspective viewof the featured section shown in FIG. 7B, the low dielectric thin filmis formed by repeatedly laminating, on the surface of the substrate in avertical position, a first porous structure domain 7 c in which columnarpores are arranged cyclically, and a second porous structure domain 7 sin which layered pores are cyclically arranged in parallel with thesurface of the substrate.

[0236] By means of such a configuration, particularly when the lowdielectric thin film is used as an interlayer dielectric film, the porescan assume a closed structure in which no opening sections are providedfor an upper layer wiring pattern or a lower layer wiring pattern. Thus,the interlayer dielectric film plays the role of a low dielectric thinfilm which has superior moisture resistance and extremely highreliability.

[0237] The other portions of the interlayer dielectric film are formedby means of the ordinary method. The switching transistor has a gateelectrode formed on the surface of the silicon substrate 1 by way of agate dielectric film 3, and a source region 5 and a drain region 6formed such that the gate electrode is sandwiched therebetween. Thelower electrode 9 is connected to the drain region 6 by way of a contact8. The source and drain regions are connected to a bit line BL.

[0238] The ferroelectric capacitor is formed from a ferroelectric thinfilm 10 which is formed from a PZT between the lower electrode 9 and anupper electrode 11.

[0239] Processes for manufacturing the FRAM will be described byreference to FIGS. 8A to 8D.

[0240] First, by means of the ordinary method, the gate electrode 4 isformed on the surface of the silicon substrate 1 by way of the gatedielectric film 3. The substrate is subjected to diffusion of impuritieswhile the gate electrode is taken as a mask, thereby forming the sourceregion 5 and the drain region 6 (FIG. 8A).

[0241] Subsequently, under the method of the invention, a mesoporoussilica thin film is formed to include a plurality of cyclic porousstructure domains containing columnar pores oriented in one direction soas to become parallel with the surface of the substrate (FIG. 8B).

[0242] Specifically, as shown in FIG. 3A, cationic cetyltrimethylammonium bromide [CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] serving as a surface activeagent; tetramethoxy silane (TMOS) serving as a silica derivative; andhydrochloric acid (HCl) serving as an acid catalyst are dissolved intoan H₂O/alcohol mixed solvent, thereby preparing a precursor solutionwithin a mixing container. Mole ratios employed for preparing the firstprecursor solution are determined such that 0.05 parts surface activeagent, 0.1 parts silica derivative, and 2 parts acid catalyst are mixedtogether with the solution being taken as 100 parts. Mole ratiosemployed for preparing the second precursor solution are determined suchthat 0.5 parts surface active agent, 1 part silica derivative, and 2parts acid catalyst are mixed together with the solution being taken as100 parts. As shown in FIG. 9, the thus-formed first and secondprecursor solutions are dropped onto the surface of the substrate 1placed on a spinner by way of respective nozzles. The substrate is spunat 500 to 5000 rpm, to thus form a mesoporous silica thin film. Themesoporous silica thin film is at 30° C. to 150° C. for one to 120hours, whereby the silica derivative is subjected to polymerizationthrough hydrolysis polycondensation reaction (a preliminary crosslinkingprocess), thereby forming a mesoporous silica thin film while a cyclicself-agglomerate of the surface active agent is taken as a mold. Here,the preliminary crosslinking process is performed preferably at 60° C.to 120° C., more preferably at 70° C. to 90° C., for about 12 to 72hours.

[0243] Finally, as in the case of the first embodiment, the substrate issintered so as to completely thermally decompose and remove the surfaceactive agent, thus forming a pure mesoporous silica thin film.

[0244] In this way, the thin film 7 of low dielectric constant of theembodiment is formed. In fact, in order to form a bit line BL, the lowdielectric thin film must be formed twice. An interlayer dielectric filmof two-layer structure having different layouts of pores may be formedby use of precursor solutions of different composition ratios before andafter formation of the bit line BL.

[0245] In the embodiment, the substrate is subjected to preliminarycrosslinking after the precursor solution has been applied over thesurface of the substrate. However, the precursor solution may be appliedover the surface of the substrate after the substrate has been subjectedto crosslinking. By means of such a configuration, the precursorsolutions hardly become mixed together and can maintain their ownstates. For this reason, an interlayer dielectric film having aplurality of cyclic porous structures can be formed more easily.

[0246] Subsequently, as shown in FIG. 8B, by means of the ordinarymethod, contact holes 8 are formed in the thin film 7 of low dielectricconstant. After plugs have been formed by embedding a highly-dopedpolycrystalline silicon layer in the respective contact holes, aniridium oxide layer is formed through use of a gas mixture consisting ofargon and oxygen while iridium is used as a target. A platinum layer isformed on the iridium oxide layer while platinum is used as a target. Inthis way, as shown in FIG. 8C, the iridium oxide layer having athickness of about 50 nm and the platinum layer having a thickness ofabout 200 nm are formed. These layers are patterned throughphotolithography, to thereby form the lower electrodes 9.

[0247] A PZT film is formed on the lower electrodes 9 as theferroelectric film 10 by means of a sol-gel method. A mixed solution ofPb (CH₃COO)₂.3H₂O, Zr (t-OC₄H₉)₄, Ti (i-OC₃H₇)₄ is used as a startingmaterial. After the mixed solution has been applied over the substratethrough spin coating, the substrate is dried at 150° C. and subjected totemporal sintering for 30 minutes at 400° C. in a dry air atmosphere.After having been repeatedly subjected to these operations five times,the substrate is subjected to heat treatment at a temperature of 700° C.or greater in an O₂ atmosphere. Thus, the ferroelectric film 10 having athickness of 250 nm is formed. Here, the PZT film is formed while “x” inPbZr_(x)Ti_(1-x)O₃ is taken as 0.52 [hereinafter expressed as PZT(52/48)] (FIG. 8D).

[0248] A laminated film 11 consisting of iridium oxide and iridium isformed on the ferroelectric film 10 by means of sputtering. Thelaminated film consisting of an iridium oxide layer and an iridium layeris taken as an upper electrode 11. The iridium layer and the iridiumoxide layer are formed to a total thickness of 200 nm. Thus, aferroelectric capacitor can be obtained, and the FRAM shown in FIG. 7 isformed.

[0249] By means of such a configuration, the interlayer dielectric filmis formed from a low dielectric thin film formed from the mesoporoussilica thin film. Hence, capacitance attributable to the interlayerdielectric film is diminished, and there can be formed FRAM whoseswitching characteristic is good and which can operate at high speed.

[0250] By virtue of a cyclic porous structure, the mechanical strengthof the dielectric film can be enhanced, and the dielectric film of highreliability can be obtained. The first porous structure domain havingcolumnar pores cyclically arranged therein and the second porousstructure domain having layered pores cyclically arranged on the surfaceof the substrate in a vertical direction are arranged repeatedly. Thepores can assume a closed structure in which no opening sections areprovided for the upper and lower wiring. The interlayer dielectric filmplays the role of a low dielectric thin film which has superior moistureresistance and high reliability. Accordingly, no leak current arises,and the interlayer dielectric film has longer life.

[0251] The composition of the first precursor solution is not limited tothe composition employed in the embodiment. Under the assumption thatthe solution assumes a value of 100, the surface active agent preferablyassumes a value of 0.01 to 0.1; the silica derivative preferably assumesa value of 0.01 to 0.5; and the acid catalyst preferably assumes a valueof 0 to 5. Use of the precursor solution having the composition enablesformation of a dielectric film of low dielectric constant havingcolumnar pores.

[0252] The composition of the second precursor solution is not limitedto that employed in the embodiment. Under the assumption that thesolution assumes a value of 100, the surface active agent preferablyassumes a value of 0.1 to 10; the silica derivative preferably assumes avalue of 0.5 to 10; and the acid catalyst preferably assumes a value of0 to 5. Use of the precursor solution having the composition enablesformation of a dielectric film of low dielectric constant having layeredpores.

[0253] In the embodiment, cationic cetyltrimethyl ammonium bromide[CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] is used as a surface active agent. It goeswithout saying that the surface active agent is not limited to such anagent and that another surface active agent may be employed.

[0254] Use of alkali ions, such as Na ions, as catalysts deteriorates asemiconductor material. Therefore, use of a cationic surface activeagent and use of an acid catalyst are preferable. In addition to HCl,nitric acid (HNO₃), sulfuric acid (H₂SO₄), phosphoric acid (H₃PO₄),H₄SO₄, or the like may also be used as the acid catalyst.

[0255] The silica derivative is not limited to TMOS. Silicon alkoxidematerial, such as tetraethoxy silane (TEOS), is preferably used.

[0256] Further, the water H₂O/alcohol mixed solvent is used as asolvent. However, it may be the case that only water is used.

[0257] Moreover, although an oxygen atmosphere is used as a sinteringatmosphere, sintering may be performed in the atmosphere, under reducedpressure, or in a nitrogen atmosphere. Preferably, use of a foaming gasformed from a gas mixture consisting of nitrogen and hydrogen enhancesmoisture resistance, thereby enabling an attempt to reduce a leakagecurrent.

[0258] A mixing ratio of the surface active agent, the silicaderivative, the acid catalyst, and the solvent can be changed asrequired.

[0259] The preliminary polymerization process is performed at 30° C. to150° C. for one through 120 hours. The temperature is desirably set to60° C. to 120° C., and more preferably to 90° C.

[0260] The sintering process is performed for one hour at 400° C.However, sintering may be performed at 300° C. to 500° C. for one tofive hours or thereabouts. Preferably, the temperature is set to 350° C.to 450° C.

FOURTH EMBODIMENT

[0261] In the first embodiment, the mesoporous silica thin film isformed by immersing the substrate into the precursor solution. However,formation of the mesoporous silica thin film is not limited toimmersion. As shown in FIG. 10, a dip coating method may also beemployed.

[0262] Specifically, the substrate is lowered to a liquid level of theprepared precursor solution at right angles at a speed of 1 mm/s through10 m/s until it sinks in the solution, and is left stationary for onesecond to one hour.

[0263] After lapse of a desired period of time, the substrate is raisedat right angles and at a rate of 1 mm/s through 10 m/s until being takenout of the solution.

[0264] Finally, as in the case of the first embodiment, the substrate issubjected to sintering, to thereby completely thermally decompose andremove the surface active agent and produce a pure mesoporous silicathin film.

[0265] At the time of formation of the precursor solution, the structureof the resultant structural body is known to change according to aproportion of the surface active agent to the silica derivative.

[0266] For instance, when a molecular ratio of the surface active agentto the silica derivative, such as CATB/TEOS, assumes a value of 0.3 to0.8, a network structure (cubic structure) is known to be obtained. Ifthe molecular ratio is lower than this molecular ratio and assumes avalue of 0.1 to 0.5, there is obtained a dielectric film of lowdielectric constant in which columnar pores are oriented. In contrast,when the molecular ratio is greater than that molecular ratio andassumes a value of 0.5 to 2, there is obtained a dielectric film of lowdielectric constant in which layered pores are oriented.

[0267] The embodiment has described the coating method using thespinner. However, a so-called brush painting method for applying asolution with a brush is also applicable.

[0268] The embodiment has described the interlayer dielectric film ofFRAM. However, the invention can also be applied to varioussemiconductor devices using silicon; a high-speed device including adevice, such as HEMT, which uses a compound semiconductor; ahigh-frequency device such as a microwave IC; highly-integratedferroelectric memory of MFMIS type; and a microwave transmission line ormultilayer wiring board using a film carrier or the like.

[0269] Particularly, an effective low dielectric thin film can beobtained as an interlayer dielectric film.

FIFTH EMBODIMENT

[0270] FRAM using a low dielectric thin film as an interlayer dielectricfilm is described as a fifth embodiment of the invention.

[0271] As shown in FIGS. 11A and 11B, the FRAM comprises a switchingtransistor fabricated in the element region enclosed with the elementisolation dielectric film 2 formed on the surface of the siliconsubstrate 1, and the ferroelectric capacitor. The invention ischaracterized by use of the thin film 7 of low dielectric constant ofthe invention as an interlayer dielectric film between the switchingtransistor and the lower electrode 9 of the ferroelectric capacitor. Asshown in an enlarged perspective view of the featuring section shown inFIG. 11B, the low dielectric thin film is formed from a mesoporoussilica thin film formed so as to include a plurality of cyclic porousstructure domains containing columnar pores “h” which are oriented inone direction so as to become parallel with the surface of thesubstrate.

[0272] The other portions of the interlayer dielectric film are formedby means of the ordinary method. The switching transistor has a gateelectrode formed on the surface of the silicon substrate 1 by way of thegate dielectric film 3, and the source region 5 and the drain region 6formed such that the gate electrode is sandwiched therebetween. Thelower electrode 9 is connected to the drain region 6 by way of thecontact 8. Source and drain regions are connected to a bit line BL.

[0273] The ferroelectric capacitor is formed from a ferroelectric thinfilm 10 which is formed from a PZT between the lower electrode 9 and theupper electrode 11.

[0274] Processes for manufacturing the FRAM will be described byreference to FIGS. 4A to 4D, which have already been described inconnection with the first embodiment.

[0275] First, under the ordinary method, the gate electrode 4 is formedon the surface of the silicon substrate 1 by way of the gate dielectricfilm 3. The substrate is subjected to diffusion of impurities while thegate electrode is taken as a mask, thereby forming the source region 5and the drain region 6 (FIG. 4A).

[0276] Subsequently, under the method of the invention, a mesoporoussilica thin film is formed to include a plurality of cyclic porousstructure domains containing columnar pores oriented in one direction soas to become parallel with the surface of the substrate (FIG. 4B).

[0277] Specifically, as shown in FIG. 2A, cationic cetyltrimethylammonium bromide [CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] serving as a surface activeagent; tetramethoxy silane (TMOS) serving as a silica derivative; andhydrochloric acid (HCl) serving as an acid catalyst are dissolved intoan H₂O/alcohol mixed solvent, thereby preparing a precursor solutionwithin a mixing container. Mole ratios employed for preparing theprecursor solution are determined such that 0.05 parts surface activeagent, 0.1 parts silica derivative, and 2 parts acid catalyst are mixedtogether with the solution being taken as 100 parts. The substrate inwhich the MOSFET is fabricated is immersed in the mixed solution. Asshown in FIG. 2B, after the mixing container has been sealed, themesoporous silica thin film is maintained at 30° C. to 150° C. for oneto 120 hours, whereby the silica derivative is subjected topolymerization through hydrolysis polycondensation reaction (apreliminary crosslinking process), thereby forming a mesoporous silicathin film while a cyclic self-agglomerate of the surface active agent istaken as a mold.

[0278] As shown in FIG. 5A, the self-agglomerate forms a sphericalmicelle structure (FIG. 5B) into which a plurality of molecules, eachcomprising C₁₆H₃₃N⁺(CH₃)₃Br⁻, coagulate. There is formed a cylindricalmember (FIG. 5E), wherein portions from which methyl groups have beendropped are hollowed (FIG. 5C) as the degree of coagulation is increasedas a result of an increase in density and wherein columnar pores areoriented.

[0279] The substrate is raised and subjected to rinsing and drying.Subsequently, the substrate is heated and sintered for three hours in anoxygen atmosphere at 400° C., thereby completely removing the surfaceactive agent remaining in a mold through thermal decomposition. A puremesoporous silica thin film is formed. In this structure, the thin filmis understood to be porous and separated into a plurality of domains,and pores are oriented in each domain.

[0280] In this way, the thin film 7 of low dielectric constant of theembodiment is formed as shown in FIG. 4B. In fact, in order to form abit line BL, the low dielectric thin film must be formed twice.

[0281] Subsequently, under the ordinary method, contact holes 8 areformed in the thin film 7 of low dielectric constant. After plugs havebeen formed by embedding a highly-doped polycrystalline silicon layer inthe respective contact holes, an iridium oxide layer is formed throughuse of a gas mixture consisting of argon and oxygen while iridium isused as a target. A platinum layer is formed on the iridium oxide layerwhile platinum is used as a target. In this way, as shown in FIG. 4C,the iridium oxide layer having a thickness of about 50 nm and theplatinum layer having a thickness of about 200 nm are formed. Theselayers are patterned through photolithography, to thereby form the lowerelectrodes 9.

[0282] The PZT film is formed on the lower electrodes 9 as theferroelectric film 10 by means of the sol-gel method. A mixed solutionof Pb (CH₃COO)₂.3H₂O, Zr (t-OC₄H₉)₄, Ti (i-OC₃H₇)₄ is used as a startingmaterial. After the mixed solution has been applied over the substratethrough spin coating, the substrate is dried at 150° C. and subjected totemporal sintering for 30 minutes at 400° C. in a dry air atmosphere.After having been repeatedly subjected to these operations five times,the substrate is subjected to heat treatment at a temperature of 700° C.or greater in an O₂ atmosphere. Thus, the ferroelectric film 10 having athickness of 250 nm is formed. Here, the PZT film is formed while “x” inPbZr_(x)Ti_(1-x)O₃ is taken as 0.52 [hereinafter expressed as PZT(52/48)] (FIG. 4D).

[0283] The laminated film 11 consisting of iridium oxide and iridium isformed on the ferroelectric film 10 by means of sputtering. Thelaminated film consisting of an iridium oxide layer and an iridium layeris taken as an upper electrode 11. The iridium layer and the iridiumoxide layer are formed to a total thickness of 200 nm. Thus, aferroelectric capacitor can be obtained, and the FRAM shown in FIG. 1 isformed.

[0284] By means of such a configuration, the interlayer dielectric filmis formed from a low dielectric thin film formed from the mesoporoussilica thin film. Hence, capacitance attributable to the interlayerdielectric film is diminished, and there can be formed FRAM whoseswitching characteristic is good and which can operate at high speed.

[0285] Since the pores are oriented so as to become parallel with thesurface of the substrate, the interlayer dielectric film possesses auniform, low dielectric constant in the direction perpendicular to thesurface of the substrate. Particularly, the interlayer dielectric filmcan assume a closed structure in which no opening sections are providedfor the lower electrode and wiring of the upper layer and the basesubstrate. The interlayer dielectric film becomes an effective lowdielectric thin film which has superior moisture resistance and highreliability. Accordingly, no leakage current arises, and the interlayerdielectric film has longer life.

[0286] The composition of the precursor solution is not limited to thecomposition employed in the embodiment. Under the assumption that thesolution assumes a value of 100, the surface active agent preferablyassumes a value of 0.01 to 0.1; the silica derivative preferably assumesa value of 0.01 to 0.5; and the acid catalyst preferably assumes a valueof 0 to 5. Use of the precursor solution having the composition enablesformation of a dielectric film of low dielectric constant havingcolumnar pores.

[0287] In the embodiment, cationic cetyltrimethyl ammonium bromide[CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] is used as a surface active agent. It goeswithout saying that the surface active agent is not limited to such anagent and that another surface active agent may be employed.

[0288] Use of alkali ions, such as Na ions, as catalysts willdeteriorate a semiconductor material. Therefore, use of a cationicsurface active agent and use of an acid catalyst are preferable. Inaddition to HCl, nitric acid (HNO₃), sulfuric acid (H₂SO₄), phosphoricacid (H₃PO₄), H₄SO₄, or the like may also be used as the acid catalyst.

[0289] The silica derivative is not limited to TMOS. Silicon alkoxidematerial, such as tetraethoxy silane (TEOS), is preferably used.

[0290] Further, the water H₂O/alcohol mixed solvent is used as asolvent. However, it may be the case that only water is used.

[0291] Moreover, although an oxygen atmosphere is used as a sinteringatmosphere, sintering may be performed in the atmosphere, under areduced pressure, or in a nitrogen atmosphere. Preferably, use of afoaming gas formed from a gas mixture consisting of nitrogen andhydrogen enhances moisture resistance, thereby enabling an attempt toreduce a leakage current.

[0292] A mixing ratio of the surface active agent, the silicaderivative, the acid catalyst, and the solvent can be changed asrequired.

[0293] The preliminary polymerization process is performed at 30° C. to150° C. for one through 120 hours. The temperature is desirably set to60° C. to 120° C., and more preferably to 90° C.

[0294] The sintering process is performed for one hour at 400° C.However, sintering may be performed at 300° C. to 500° C. for one tofive hours or thereabouts. Preferably, the temperature is set to 350° C.to 450° C.

SIXTH EMBODIMENT

[0295] A structure in which the pores “h” are oriented in the form of alayer as shown in FIG. 12F is also effective. Here, the structure isformed by further increasing the density of the surface active agent inthe precursor solution. In other respects, the processes are the same asthose employed in the fifth embodiment.

[0296] When the density of the surface active agent in the structureshown in FIG. 4C is increased, molecules are oriented in the form of alayer as shown in FIG. 4D, whereby a dielectric film of low dielectricconstant in which the pores “h” are oriented in the form of a layer asshown in FIG. 4F is formed. Such a structure has a percentage of poreshigher than that of the structure having columnar pores and henceenables a decrease in dielectric constant.

[0297] At the time of formation of the precursor solution, the structureof the resultant structural body is known to change according to theproportion of the surface active agent to the silica derivative.

[0298] For instance, when a molecular ratio of the surface active agentto the silica derivative, such as CATB/TEOS, assumes a value of 0.3 to0.8, a three-dimensional network structure (cubic structure) is known tobe obtained. If the molecular ratio is lower than this molecular ratioand assumes a value of 0.1 to 0.5, there is obtained a dielectric filmof low dielectric constant in which columnar pores are oriented. Incontrast, when the molecular ratio is greater than that molecular ratioand assumes a value of 0.5 to 2, there is obtained a dielectric film oflow dielectric constant in which layered pores are oriented.

[0299] The embodiment has described the coating method using thespinner. However, a so-called brush painting method for applying asolution with a brush is also applicable.

SEVENTH EMBODIMENT

[0300] A semiconductor device of multilayer wiring structure using thelow dielectric thin film as an interlayer dielectric film will bedescribed as a seventh embodiment of the invention.

[0301] As shown in FIGS. 13, 15G, and 15H, the semiconductor device ischaracterized in that an interlayer dielectric film is formed from aninorganic dielectric film having a porous structure, in which a framesurrounding the pores “h” are coated with a hydrophobic layer S. FIGS.15G and 15H are enlarged descriptive views showing the porous structureof an interlayer dielectric film employed herein. In this embodiment,the semiconductor device is characterized as follows. Specifically, inorder to |form a more effective interlayer dielectric film, theinterlayer dielectric film is formed from a dielectric film having atwo-layer structure and a low dielectric constant. A first interlayerdielectric film 13 a having the contact holes H to contact the firstwiring layer 12 is formed from a second porous structure domain, whereinthe layered pores “h” are arranged cyclically so as to become parallelwith the surface of the substrate, and a framework surrounding the pores“h” is coated with the hydrophobic layer S. The second interlayerdielectric film 13 b—which is charged in an inter-wiring region of theupper-layer-side second wiring layer 14 formed on the first interlayerdielectric film 13 a—is formed from the first porous structure domain inwhich columnar pores are arranged cyclically, and the frameworksurrounding the pores “h” is coated with the hydrophobic layer S.

[0302] Specifically, a lower layer portion of the interlayer dielectricfilm—which is formed between the first wiring layer 12 formed on thesurface of an element region enclosed with the element isolationdielectric film (not shown) formed on the surface of the siliconsubstrate 1S and the second wiring layer 14—is taken as the firstinterlayer dielectric film 13 a in which layered pores are arrangedcyclically so as to become parallel with the surface of the substrate.The second interlayer dielectric film 13 b—which serves as an upperlayer side and is formed in a region between wiring patterns of thesecond wiring layer as an inter-line dielectric film—is formed from afirst porous structure domain in which columnar pores are arrangedcyclically.

[0303] The other portions of the semiconductor device are of ordinarystructure, and their illustrations and explanations are omitted.

[0304] Processes for manufacturing the interlayer dielectric film willnow be described by reference to FIGS. 14A to 14D.

[0305] First, as shown in FIG. 14A, a desired semiconductor region isformed on the surface of a silicon substrate 1S by means of an ordinarymethod, thereby forming the first wiring layer 12.

[0306] Subsequently, by means of the method of the invention, amesoporous silica thin film is formed from a second cyclic porousstructure domain, wherein the layered pores are arranged cyclically soas to become parallel with the surface of the substrate, and a frameworksurrounding the pores is coated with a hydrophobic layer (FIG. 14B).

[0307] Specifically, as shown in FIG. 3A, cationic cetyltrimethylammonium bromide [CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] serving as a surface activeagent; tetramethoxy silane (TMOS) serving as a silica derivative; andhydrochloric acid (HCl) serving as an acid catalyst a redissolved intothe H₂O/alcohol mixed solvent, thereby preparing a precursor solutionwithin the mixing container. Mole ratios employed for preparing theprecursor solution are determined such that 0.5 parts surface activeagent, 1 part silica derivative, and 2 parts acid catalyst are mixedtogether with the solution being taken as 100 parts. A substrate havingthe first wiring layer 12 formed thereon is immersed in the mixture ofsolutions. As shown in FIG. 3B, after the mixing container has beensealed, the mixture is maintained at 30° C. to 150° C. for one to 120hours, whereby the silica derivative is subjected to polymerizationthrough hydrolysis polycondensation reaction (a preliminary crosslinkingprocess), thereby forming a cyclic self-agglomerate of the surfaceactive agent.

[0308] As shown in FIG. 15A, the self-agglomerate forms a sphericalmicelle structure (FIG. 15B) into which a plurality of molecules, eachcomprising C₁₆H₃₃N⁺(CH₃)₃Br⁻, coagulate. There is formed a laminatedstructure (FIG. 15D) in which the surface active agent is oriented asthe density increases (FIG. 15C).

[0309] The substrate is raised and subjected to rinsing and drying.Subsequently, the substrate is heated and sintered for three hours in anoxygen atmosphere at 400° C., thereby completely removing the surfaceactive agent remaining in the mold through thermal decomposition. Apure, mesoporous silica thin film is formed.

[0310] Subsequently, the mesoporous silica thin film is exposed to steamof trimethyl-chloro-silane or triethyl-chloro-silane. The thus-exposedthin film is left for 24 hours at 90° C. to 300° C. As shown in FIG.14B, there is formed the first interlayer dielectric film 13 a, whereinthe layered pores parallel to the surface of the substrate are arranged,and the framework surrounding the pores is coated with the hydrophobiclayer. FIG. 15H shows an enlarged descriptive view of the firstinterlayer dielectric film. Here, the high-density self-agglomerate suchas that shown in FIG. 15D is formed and sintered, whereby an inorganicdielectric film, such as that shown in FIG. 15F, in which layered poresa rearranged can be formed. As shown in FIG. 15H, the thus-formedinorganic dielectric film is sililated, thereby forming the interlayerdielectric film 13 a whose framework surrounding the pores “h” is coatedwith the hydrophobic layer S. A reaction formula achieved at this timeis as follows:

Si—OH+Si(CH₃)₃Cl→Si—O—Si(CH₃)₃+HCl

[0311] As shown in FIG. 14C, the through holes H are formed in the firstinterlayer dielectric film 13 a, and the second wiring layer 14 isformed by means of the ordinary method.

[0312] Subsequently, the second interlayer dielectric film 13 b isformed. The second interlayer dielectric film is formed in the samemanner as in the process for forming the first interlayer dielectricfilm 13 a. However, there is employed a precursor solution whosecomposition is changed from that of the precursor solution employed forforming the first interlayer dielectric film. Here, mole ratios employedfor preparing the precursor solution are determined such that 0.05 partssurface active agent, 0.1 parts silica derivative, and 2 parts acidcatalyst are mixed together with the solution being taken as 100 parts.In other respects, the second interlayer dielectric film is formed intotally the same manner as that employed for forming the firstinterlayer dielectric film.

[0313] As shown in FIG. 14D, there is obtained the second interlayerdielectric film 13 b formed from the first porous structure domain,wherein columnar pores are cyclically arranged and the frameworksurrounding the pores “h” is coated with the hydrophobic layer S.

[0314] Here, the spherical micelle structure into which a plurality ofmolecules, each comprising C₁₆H₃₃N⁺(CH₃)₃Br⁻, coagulate is furtherincreased in density, thereby forming a cylindrical substance in whichpores are oriented. Thus, a self-agglomerate such as that shown in FIG.15C is formed and sintered. Thus, there is obtained the secondinterlayer dielectric film 13 b formed from the first porous structuredomain, such as that shown in FIG. 15E, wherein columnar pores arecyclically arranged. The second interlayer dielectric film is sililated,thereby forming the interlayer dielectric film 13 b whose frameworksurrounding the pores “h” is coated with the hydrophobic layer S, asshown in FIG. 15G.

[0315]FIG. 16 is a structural descriptive view showing a cross sectionof the substrate in this state. As is evident from the drawing, themultilayer wiring structure is understood to comprise the firstinterlayer dielectric film 13 a formed from a porous thin film, in whichthe pores are formed in a layered form and the framework surroundingpores “h” is coated with the hydrophobic layer S; and the secondinterlayer dielectric film 13 b, in which columnar pores are cyclicallyarranged and the framework surrounding the pores “h” is coated with thehydrophobic layer S.

[0316] In relation to the semiconductor device having the thus-formedmultilayer wiring structure, the first interlayer dielectric film 13 aconstitutes, in the region surrounding the contact holes H, the secondporous structure domain in which the layered pores are arrangedcyclically and the framework surrounding the pores “h” is coated withthe hydrophobic layer S. Hence, the interlayer capacitance can bediminished. Further, the columnar pores are arranged between wiringpatterns within the upper layer wiring region constituting theinter-wiring dielectric film, and hence inter-wiring capacitance islowered. In the second interlayer dielectric film 13 b constituting theinter-wiring dielectric film, the columnar pores are oriented so as tobecome parallel with the direction in which a wiring pattern of thesecond wiring layer 14 is arranged, and the framework surrounding thepores “h” is coated with the hydrophobic layer S. Hence, there can beprovided a semiconductor device having high reliability withoutinvolvement of a problem of occurrence of a short circuit between wiringpatterns.

EIGHTH EMBODIMENT

[0317] In the seventh embodiment, the interlayer dielectric film isformed from a dielectric film having a two-layer structure and a lowdielectric constant. A lower layer portion of the interlayer dielectricfilm is formed from the second porous structure domain, in which layeredpores are arranged cyclically so as to become parallel with the surfaceof the substrate, and the framework surrounding the pores is coated withthe hydrophobic layer. An upper layer portion of the interlayerdielectric film is formed from the first porous structure domain inwhich the columnar pores are arranged cyclically and the frameworksurrounding the pores is coated with the hydrophobic layer. However, theupper layer portion of the interlayer dielectric film may be formed froma third porous structure domain which is perpendicular to the surface ofthe substrate and runs in parallel with a main wiring pattern, insteadof the porous structure domain having the columnar pores.

[0318] The structure of the third porous structure domain is shown inFIG. 17. As shown in FIG. 17, the semiconductor device is characterizedin that the interlayer dielectric film is formed from a low dielectricfilm of two-layer structure; in that the first interlayer dielectricfilm 13 a having the contact holes H that contact the first wiring layer11 is formed from the second porous structure domain, in which layeredpores are arranged cyclically so as to become parallel with the surfaceof the substrate, and the framework surrounding the pores is coated withthe hydrophobic layer; and in that the second interlayer dielectric film13S which is to be formed on the first interlayer dielectric film 13 a,serves as an upper layer portion, and is charged into the inter-wiringregion of the second wiring layer 14 is formed from the third porousstructure domain, in which columnar pores are arranged cyclically andthe framework surrounding the pores “h” is coated with the hydrophobiclayer S.

[0319] Specifically, a lower layer portion of the interlayer dielectricfilm—which is formed between the first wiring layer 12 formed on thesurface of an element region enclosed with the element isolationdielectric film (not shown) formed on the surface of the siliconsubstrate 11 and the second wiring layer 14—is taken as the firstinterlayer dielectric film 13 a in which layered pores are arrangedcyclically so as to become parallel with the surface of the substrate.The second interlayer dielectric film 13S which serves as an upper layerportion and is formed in a region between wiring patterns of the secondwiring layer as an inter-line dielectric film is formed from the thirdporous structure domain which is perpendicular to the surface of thesubstrate and runs in parallel with the main wiring pattern.

[0320] The other portions of the semiconductor device are formed intotally the same manner as in the case of the first embodiment, andtheir illustrations and explanations are omitted.

[0321] By means of such a configuration, the inter-wiring capacitancecan be lowered further. Since the third porous structure domain runs inparallel with the main wiring pattern, a multilayer insulation wall ispresent between wiring patterns, whereby occurrence of a short circuitbetween wiring patterns can be prevented more reliably.

NINTH EMBODIMENT

[0322] FRAM using a low dielectric thin film as an interlayer dielectricfilm is described as a ninth embodiment of the invention.

[0323] As shown in FIG. 18A, the FRAM comprises a switching transistorfabricated in the element region enclosed with the element isolationdielectric film 2 formed on the surface of the silicon substrate 1, anda ferroelectric capacitor. The invention is characterized by use of thethin film 7 of low dielectric constant of the invention as an interlayerdielectric film between the switching transistor and the lower electrode9 of the ferroelectric capacitor. As shown in an enlarged perspectiveview of the featured section shown in FIG. 18B, the low dielectric thinfilm is characterized by repeated stacking, perpendicular to the surfaceof the substrate, the first porous structure domain 7 c, in whichcolumnar pores are arranged cyclically and the framework surrounding thepores “h” is coated with the hydrophobic layer S; and the second porousstructure domain 7 s, in which layered pores are cyclically arranged inparallel with the surface of the substrate and the framework surroundingthe pores “h” is coated with the hydrophobic layer S.

[0324] By means of such a configuration, particularly when the lowdielectric thin film is used as an interlayer dielectric film, thedielectric film can assume a closed structure in which no openingsections are provided for an upper layer wiring pattern or a lower layerwiring pattern. Thus, the interlayer dielectric film plays the role of alow dielectric thin film which has superior moisture resistance andextremely high reliability.

[0325] The other portions of the interlayer dielectric film are formedby the ordinary method. The switching transistor has a gate electrodeformed on the surface of the silicon substrate 1 by way of the gatedielectric film 3, and a source region 5 and a drain region 6 formedsuch that the gate electrode is sandwiched therebetween. The lowerelectrode 9 is connected to the drain region 6 by way of a contact 8.The source region 5 is connected to a bit line BL.

[0326] The ferroelectric capacitor is formed from the ferroelectric thinfilm 10 which is formed from a PZT between the lower electrode 9 and theupper electrode 11.

[0327] Processes for manufacturing the FRAM will be described byreference to FIGS. 8A to 8D described in connection with the thirdembodiment.

[0328] First, under the ordinary method, the gate electrode 4 is formedon the surface of the silicon substrate 1 by way of the gate dielectricfilm 3. The substrate is subjected to diffusion of impurities while thegate electrode is taken as a mask, thereby forming the source region 5and the drain region 6 (FIG. 8A).

[0329] Subsequently, under the method of the invention, a mesoporoussilica thin film is formed to include a plurality of cyclic porousstructure domains containing columnar pores oriented in one direction soas to become parallel with the surface of the substrate (FIG. 8B).

[0330] Specifically, as shown in FIG. 3A, cationic cetyltrimethylammonium bromide [CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] serving as a surface activeagent; tetramethoxy silane (TMOS) serving as a silica derivative; andhydrochloric acid (HCl) serving as an acid catalyst are dissolved intoan H₂O/alcohol mixed solvent, thereby preparing a precursor solutionwithin a mixing container. Mole ratios employed for preparing the firstprecursor solution are determined such that 0.05 parts surface activeagent, 0.1 parts silica derivative, and 2 parts acid catalyst are mixedtogether with the solution being taken as 100 parts. Mole ratiosemployed for preparing the second precursor solution are determined suchthat 0.5 parts surface active agent, 1 part silica derivative, and 2parts acid catalyst are mixed together with the solution being taken as100 parts. As shown in FIG. 9, the thus-formed first and secondprecursor solutions are dropped onto the surface of the substrate 1placed on a spinner by way of respective nozzles. The substrate is spunat 500 to 5000 rpm, to thus form a mesoporous silica thin film. Themesoporous silica thin film is maintained at a temperature of 30° C. to150° C. for one to 120 hours, whereby the silica derivative is subjectedto polymerization through hydrolysis polycondensation reaction (apreliminary crosslinking process), thereby forming a mesoporous silicathin film while a cyclic self-agglomerate of the surface active agent istaken as a mold. Here, the preliminary crosslinking process is performedpreferably at 60° C. to 120° C., more preferably at 70° C. to 90° C.,for about 12 to 72 hours.

[0331] As in the case of the seventh embodiment, the substrate issintered to completely thermally decompose and remove the surface activeagent, thus forming a pure mesoporous silica thin film. Finally, themesoporous silica thin film is exposed to steam oftrimethyl-chloro-silane or triethyl-chloro-silane. The thus-exposed thinfilm is left for a few minutes to several days at 90° C. to 300° C.,thereby coating the framework surrounding the pores “h” with thehydrophobic layer S.

[0332] In this way, as shown in FIG. 8B, the thin film 7 of lowdielectric constant of the embodiment is formed. In fact, in order toform the bit line BL, the low dielectric thin film must be formed twice.An interlayer dielectric film of two-layer structure having differentlayouts of pores may be formed by use of precursor solutions ofdifferent composition ratios before and after formation of the bit lineBL.

[0333] In the embodiment, the substrate is subjected to preliminarycrosslinking after the precursor solution has been applied over thesurface of the substrate. However, the precursor solution may be appliedover the surface of the substrate after the substrate has been subjectedto crosslinking. By means of such a configuration, the precursorsolutions hardly become mixed together and can maintain their ownstates. For this reason, an interlayer dielectric film having aplurality of cyclic porous structures can be formed more easily.

[0334] Subsequently, by means of the ordinary method, contact holes 8are formed in the thin film 7 of low dielectric constant. After plugshave been formed by embedding a highly-doped polycrystalline siliconlayer in the respective contact holes, an iridium oxide layer is formedthrough use of a gas mixture consisting of argon and oxygen whileiridium is used as a target. A platinum layer is formed on the iridiumoxide layer while platinum is used as a target. In this way, as shown inFIG. 8C, the iridium oxide layer having a thickness of about 50 nm andthe platinum layer having a thickness of about 200 nm are formed. Theselayers are patterned through photolithography, to thereby form the lowerelectrodes 9.

[0335] A PZT film is formed on the lower electrodes 9 as theferroelectric film 10 by means of the sol-gel method. A mixed solutionof Pb(CH₃COO)₂.3H₂O, Zr (t-OC₄H₉)₄, Ti(i-OC₃H₇)₄ is used as a startingmaterial. After the mixed solution has been applied over the substratethrough spin coating, the substrate is dried at 150° C. and subjected totemporal sintering for 30 minutes at 400° C. in a dry air atmosphere.After having been repeatedly subjected to these operations five times,the substrate is subjected to heat treatment at a temperature of 700° C.or greater in an O₂ atmosphere. Thus, the ferroelectric film 10 having athickness of 250 nm is formed. Here, the PZT film is formed while “x” inPbZr_(x)Ti_(1-x)O₃ is taken as 0.52 [hereinafter expressed as PZT(52/48)] (FIG. 8D).

[0336] A laminated film 11 consisting of iridium oxide and iridium isformed on the ferroelectric film 10 by means of sputtering. Thelaminated film consisting of an iridium oxide layer and an iridium layeris taken as an upper electrode 11. The iridium layer and the iridiumoxide layer are formed to a total thickness of 200 nm. Thus, aferroelectric capacitor can be obtained, and the FRAM shown in FIG. 18is formed.

[0337] By means of such a configuration, the interlayer dielectric filmis formed from a low dielectric thin film formed from the mesoporoussilica thin film. Hence, capacitance attributable to the interlayerdielectric film is diminished, and there can be formed FRAM whoseswitching characteristic is good and which can operate at high speed.

[0338] By virtue of a cyclic porous structure, the mechanical strengthof the dielectric film can be enhanced, and the dielectric film havinghigh reliability can be obtained.

[0339] Since the framework surrounding the pores is coated with thehydrophobic layer, a structure having higher moisture resistance can beobtained. Moreover, the first porous structure domain having columnarpores cyclically arranged therein and the second porous structure domainhaving layered pores cyclically arranged on the surface of the substratein a vertical direction are arranged repeatedly. The pores can assume aclosed structure in which no opening sections are provided for the upperand lower wiring. The interlayer dielectric film plays the role of a lowdielectric thin film which has superior moisture resistance and highreliability. Accordingly, no leakage current arises, and the interlayerdielectric film has longer life.

[0340] The composition of the first precursor solution is not limited tothe composition employed in the embodiment. Under the assumption thatthe solution assumes a value of 100, the surface active agent preferablyassumes a value of 0.01 to 0.1; the silica derivative preferably assumesa value of 0.01 to 0.5; and the acid catalyst preferably assumes a valueof 0 to 5. Use of the precursor solution having the composition enablesformation of a dielectric film of low dielectric constant havingcolumnar pores.

[0341] The composition of the second precursor solution is not limitedto that employed in the embodiment. Under the assumption that thesolution assumes a value of 100, the surface active agent preferablyassumes a value of 0.1 to 10; the silica derivative preferably assumes avalue of 0.5 to 10; and the acid catalyst preferably assumes a value of0 to 5. Use of the precursor solution having the composition enablesformation of a dielectric film of low dielectric constant having layeredpores.

[0342] In the embodiment, cationic cetyltrimethyl ammonium bromide[CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] is used as a surface active agent. It goeswithout saying that the surface active agent is not limited to such anagent, and another surface active agent may be employed.

[0343] Use of alkali ions, such as Na ions, as catalysts willdeteriorate a semiconductor material. Therefore, use of a cationicsurface active agent and use of an acid catalyst are preferable. Inaddition to HCl, nitric acid (HNO₃), sulfuric acid (H₂SO₄), phosphoricacid (H₃PO₄), H₄SO₄, or the like may also be used as the acid catalyst.

[0344] The silica derivative is not limited to TMOS. Silicon alkoxidematerial, such as tetraethoxy silane (TEOS), is preferably used.

[0345] Further, the water H₂O/alcohol mixed solvent is used as asolvent. However, it may be the case that only water is used.

[0346] Moreover, although a nitrogen atmosphere is used as a sinteringatmosphere, sintering maybe performed under a reduced pressure or in theatmosphere. Preferably, addition of sintering involving usage of afoaming gas formed from a gas mixture consisting of nitrogen andhydrogen enhances moisture resistance, thereby enabling an attempt toreduce a leakage current.

[0347] A mixing ratio of the surface active agent, the silicaderivative, the acid catalyst, and the solvent can be changed asrequired.

[0348] The preliminary polymerization process is held at 30° C. to 150°C. for one through 120 hours. The temperature is desirably set to 60° C.to 120° C., more preferably to 90° C.

[0349] The sintering process is performed for one hour at 400° C.However, sintering may be performed at 300° C. to 500° C. for one tofive hours or thereabouts. Preferably, the temperature is set to 350° C.to 450° C.

[0350] The sililation process is performed by exposing the mesoporoussilica thin film to a steam of sililation agent. However, needless tosay, a solution or mist may also be employed.

TENTH EMBODIMENT

[0351] In the ninth embodiment, the mesoporous silica thin film isformed by immersing the substrate into the precursor solution. However,formation of the mesoporous silica thin film is not limited toimmersion. As shown in FIG. 10, a dip coating method may also beemployed.

[0352] Specifically, the substrate is lowered to a liquid level of theprepared precursor solution at right angles at a speed of 1 mm/s through10 m/s until it sinks in the solution, and is left stationary for onesecond to one hour.

[0353] After lapse of a desired period of time, the substrate is raisedat right angles and at a rate of 1 mm/s through 10 m/s until being takenout of the solution.

[0354] As in the case of the ninth embodiment, the substrate issubjected to sintering, to thereby completely thermally decompose andremove the surface active agent and produce a pure mesoporous silicathin film. Finally, the substrate is subjected to sililation, to therebyform a mesoporous silica thin film whose framework surrounding the pores“h” is coated with the hydrophobic layer S.

[0355] When CATB is used as the surface active agent and TEOS is used asthe silica derivative, the structure of the resultant structural body isknown to change according to a proportion of the surface active agent tothe silica derivative.

[0356] For instance, when a molecular ratio of the surface active agentto the silica derivative, such as CATB/TEOS, assumes a value of 0.3 to0.8, a network structure (cubic structure) is known to be obtained. Ifthe molecular ratio is lower than this molecular ratio and assumes avalue of 0.1 to 0.5, there is obtained a dielectric film of lowdielectric constant in which columnar pores are oriented. In contrast,when the molecular ratio is greater than that molecular ratio andassumes a value of 0.5 to 2, there is obtained a dielectric film of lowdielectric constant in which layered pores are oriented.

[0357] The embodiment has described the interlayer dielectric film ofFRAM. However, the invention can also be applied to varioussemiconductor devices using silicon; a high-speed device including adevice, such as HEMT, which uses a compound semiconductor; ahigh-frequency device such as a microwave IC; highly-integratedferroelectric memory of MFMIS type; and a microwave transmission line ormultilayer wiring board using a film carrier or the like.

[0358] As has been described, according to the invention, there isconstituted an inorganic dielectric film of porous structure whoseframework surrounding the pores “h” is coated with a hydrophobic layer.Hence, a dielectric film which is easily controllable and has highmechanical strength and a low dielectric constant can be obtained.

[0359] Particularly, an effective low dielectric thin film can beobtained as an interlayer dielectric film.

ELEVENTH EMBODIMENT

[0360] FRAM using a low dielectric thin film as an interlayer dielectricfilm is described as an eleventh embodiment of the invention.

[0361] As shown in FIGS. 19A and 19B, the FRAM comprises a switchingtransistor fabricated in the element region enclosed with the elementisolation dielectric film 2 formed on the surface of the siliconsubstrate 1, and the ferroelectric capacitor. The invention ischaracterized by use of the thin film 7 of low dielectric constant ofthe invention as an interlayer dielectric film between the switchingtransistor and the lower electrode 9 of the ferroelectric capacitor. Asshown in an enlarged perspective view of the featured section shown inFIG. 19B, the low dielectric thin film is formed from a mesoporoussilica thin film formed so as to assume a porous structure which isformed on the surface of the substrate and has the pores “h,” eachhaving a three-dimensional network structure.

[0362] The other portions of the interlayer dielectric film are formedby means of the ordinary method. The switching transistor has the gateelectrode 4 formed on the surface of the silicon substrate 1 by way ofthe gate dielectric film 3, and the source region 5 and the drain region6 formed such that the gate electrode 4 is sandwiched therebetween. Thelower electrode 9 is connected to the drain region 6 by way of thecontact 8. Source and drain regions are connected to a bit line BL.

[0363] The ferroelectric capacitor is formed from a ferroelectric thinfilm 10 which is formed from a PZT between the lower electrode 9 and theupper electrode 11.

[0364] Processes for manufacturing the FRAM will be described byreference to the drawings shown in FIGS. 8A to 8D.

[0365] First, by means of the ordinary method, the gate electrode 4 isformed on the surface of the silicon substrate 1 by way of the gatedielectric film 3. The substrate is subjected to diffusion of impuritieswhile the gate electrode 4 is taken as a mask, thereby forming thesource region 5 and the drain region 6 (FIG. 8A).

[0366] Subsequently, under the method of the invention, a mesoporoussilica thin film is formed to include the porous structure having thepores, each having a three-dimensional network structure (FIG. 8B).

[0367] Specifically, as shown in FIG. 2A, cationic cetyltrimethylammonium bromide [CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] serving as a surface activeagent; tetramethoxy silane (TMOS) serving as a silica derivative; andhydrochloric acid (HCl) serving as an acid catalyst are dissolved intoan H₂O/alcohol mixed solvent, thereby preparing a precursor solutionwithin a mixing container. Mole ratios employed for preparing theprecursor solution were determined such that 0.02 parts surface activeagent, 0.4 parts silica derivative, and 2 parts acid catalyst are mixedtogether with the solution being taken as 100 parts. As shown in FIG.2B, after the mixing container has been sealed, the mesoporous silicathin film is maintained at 30° C. to 150° C. for one to 120 hours,whereby the silica derivative is subjected to polymerization throughhydrolysis polycondensation reaction (a preliminary crosslinkingprocess), thereby forming a mesoporous silica thin film while a cyclicself-agglomerate of the surface active agent is taken as a mold.

[0368] As shown in FIG. 4A, the self-agglomerate forms a sphericalmicelle structure (FIG. 4B) into which a plurality of molecules, eachcomprising C₁₆H₃₃N⁺(CH₃)₃Br⁻, coagulate. There is formed a cylindricalmember (FIG. 4E), wherein the surface active agent is oriented as thedensity increases (FIG. 4C). The cylindrical member is furthertransformed into a three-dimensional network cylindrical member througha phase change.

[0369] The substrate is raised and subjected to rinsing and drying.Subsequently, the substrate is heated and sintered for three hours in anoxygen atmosphere at 400° C., thereby completely removing the surfaceactive agent remaining in the mold through thermal decomposition. A puremesoporous silica thin film having a three-dimensional network isformed. Consideration must be paid to the sintering atmosphere.

[0370] In this way, the thin film 7 of low dielectric constant of theembodiment is formed as shown in FIG. 8B. In fact, in order to form abit line BL, the low dielectric thin film must be formed twice.

[0371] Subsequently, by means of the ordinary method, contact holes 8are formed in the thin film 7 of low dielectric constant. After plugshave been formed by embedding a highly-doped polycrystalline siliconlayer in the respective contact holes, an iridium oxide layer is formedthrough use of a gas mixture consisting of argon and oxygen whileiridium is used as a target. A platinum layer is formed on the iridiumoxide layer while platinum is used as a target. In this way, as shown inFIG. 8C, the iridium oxide layer having a thickness of about 50 nm andthe platinum layer having a thickness of about 200 nm are formed. Theselayers are patterned through photolithography, to thereby form the lowerelectrodes 9.

[0372] The PZT film is formed on the lower electrodes 9 as theferroelectric film 10 by means of the sol-gel method. A mixed solutionof Pb (CH₃COO)₂.3H₂O, Zr (t-OC₄H₉)₄, Ti (i-OC₃H₇)₄ is used as a startingmaterial. After the mixed solution has been applied over the substratethrough spin coating, the substrate is dried at 150° C. and subjected totemporal sintering for 30 minutes at 400° C. in a dry air atmosphere.After having been repeatedly subjected to these operations five times,the substrate is subjected to heat treatment at a temperature of 700° C.or greater in an O₂ atmosphere. Thus, the ferroelectric film 10 having athickness of 250 nm is formed. Here, the PZT film is formed while “x” inPbZr_(x)Ti_(1-x)O₃ is taken as, 0.52 [hereinafter expressed as PZT(52/48)] (FIG. 8D).

[0373] The laminated film 11 consisting of iridium oxide and iridium isformed on the ferroelectric film 10 by means of sputtering. Thelaminated film consisting of an iridium oxide layer and an iridium layeris taken as an upper electrode 11. The iridium layer and the iridiumoxide layer are formed to a total thickness of 200 nm. Thus, aferroelectric capacitor can be obtained, and the FRAM shown in FIG. 19is formed.

[0374] By means of such a configuration, the interlayer dielectric filmis formed from a low dielectric thin film formed from the mesoporoussilica thin film that has a three-dimensional network structure. Hence,capacitance attributable to the interlayer dielectric film isdiminished, and there can be formed FRAM whose switching characteristicis good and which can operate at high speed.

[0375] Since the pores are formed on the surface of the substrate so asto assume a three-dimensional network structure, a uniform, lowdielectric constant is achieved over the entire surface of thesubstrate. Particularly, the interlayer dielectric film can assume aclosed structure in which no opening sections are provided for the lowerelectrode and wiring of the upper layer and the base substrate. Theinterlayer dielectric film becomes an effective low dielectric thin filmwhich has superior moisture resistance and high reliability.Accordingly, no leakage current arises, and the interlayer dielectricfilm has longer life.

[0376] The composition of the precursor solution is not limited to thecomposition employed in the embodiment. Under the assumption that thesolution assumes a value of 100, the surface active agent preferablyassumes a value of 0.05 to 0.5; the silica derivative preferably assumesa value of 0.1 to 1; and the acid catalyst preferably assumes a value of0 to 5. Use of the precursor solution having the composition enablesformation of a dielectric film of low dielectric constant having poresof three-dimensional network structure.

[0377] When CATB is used as a surface active agent and TEOS is used as asilica derivative, the structure of the resultant structural body isknown to change according to a proportion of the surface active agent tothe silica derivative.

[0378] For instance, when a molecular ratio of the surface active agentto the silica derivative, such as CATB/TEOS, assumes a value of 0.3 to0.8, a network structure (cubic structure) is known to be obtained. Ifthe molecular ratio is lower than this molecular ratio, there isobtained a dielectric film of low dielectric constant in which columnarpores are oriented. In contrast, when the molecular ratio is greaterthan that molecular ratio, there is obtained a dielectric film of lowdielectric constant in which layered pores are oriented.

[0379] In the embodiment, cationic cetyltrimethyl ammonium bromide[CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] is used as a surface active agent. It goeswithout saying that the surface active agent is not limited to such anagent, and another surface active agent may be employed.

[0380] Use of alkali ions, such as Na ions, as catalysts willdeteriorate a semiconductor material. Therefore, use of a cationicsurface active agent and use of an acid catalyst are preferable. Inaddition to HCl, nitric acid (HNO₃), sulfuric acid (H₂SO₄), phosphoricacid (H₃PO₄), H₄SO₄, or the like may also be used as the acid catalyst.

[0381] The silica derivative is not limited to TMOS. Silicon alkoxidematerial, such as tetraethoxy silane (TEOS), is preferably used.

[0382] Further, the water H₂O/alcohol mixed solvent is used as asolvent. However, it may be the case that only water is used.

[0383] Moreover, although an oxygen atmosphere is used as a sinteringatmosphere, sintering may be performed in the atmosphere, under areduced pressure, or in a nitrogen atmosphere. Preferably, additionalsintering involving usage of a foaming gas formed from a gas mixtureconsisting of nitrogen and hydrogen enhances moisture resistance,thereby enabling an attempt to reduce a leakage current.

[0384] A mixing ratio of the surface active agent, the silicaderivative, the acid catalyst, and the solvent can be changed asrequired.

[0385] The preliminary polymerization process is performed at 30° C. to150° C. for one through 120 hours. The temperature is desirably set to60° C. to 120° C., more preferably to 90° C.

[0386] The sintering process is performed for one hour at 400° C.However, sintering may be performed at 300° C. to 500° C. from one tofive hours or thereabouts. Preferably, the temperature is set to 350° C.to 450° C.

[0387] As shown in FIG. 1C, so long as there is formed the inorganicdielectric film having the pores “h” of periodic three-dimensionalnetwork structure, the dielectric constant can be made more uniform.

TWELFTH EMBODIMENT

[0388] In the eleventh embodiment, the mesoporous silica thin film isformed by immersing the substrate into the precursor solution. However,formation of the mesoporous silica thin film is not limited toimmersion. As shown in FIG. 10, a dip coating method may also beemployed.

[0389] Specifically, the substrate is lowered to a liquid level of theprepared precursor solution at right angles at a speed of 1 mm/s through10 m/s until it sinks in the solution, and is left stationary for zerosecond to one hour.

[0390] After lapse of a desired period of time, the substrate is raisedat right angles and at a rate of 1 mm/s through 10 m/s until being takenout of the solution.

[0391] Finally, as in the case of the first embodiment, the substrate issubjected to sintering, to thereby completely thermally decompose andremove the surface active agent and produce a pure mesoporous silicathin film formed from pores of three-dimensional network structure.

THIRTEENTH EMBODIMENT

[0392] In the first embodiment, the mesoporous silica thin film isformed by immersing the substrate into the precursor solution. However,formation of the mesoporous silica thin film is not limited toimmersion. As shown in FIG. 9, a spin coating method may also beemployed.

[0393] The precursor solution formed in the same manner as in theembodiment is dropped onto the surface of the substrate to be processedplaced on the spinner. The substrate is then spun at 500 to 5000 rpm,thus forming a mesoporous silica thin film.

[0394] Finally, as in the case of the first embodiment, the substrate issubjected to sintering, to thereby completely thermally decompose andremove the surface active agent and produce a pure mesoporous silicathin film formed from pores of three-dimensional network structure.

[0395] By means of such a structure, the porous structure formed fromthe pores of three-dimensional network structure enhances mechanicalstrength of the dielectric film, and the dielectric film having highreliability can be obtained. When being used as an interlayer dielectricfilm, the mesoporous silica thin film assumes a closed structure inwhich no opening sections are provided for the upper and lower wiring.The interlayer dielectric film plays the role of a low dielectric thinfilm which has superior moisture resistance and high reliability.

[0396] The embodiment has described the coating method using thespinner. However, a so-called brush painting method for applying asolution with a brush is also applicable.

[0397] As has been described above, the invention enables easy formationof a porous structure having pores of three-dimensional networkstructure with superior controllability so that a dielectric film havinghigh mechanical strength and a low dielectric constant can be obtained.

FOURTEENTH EMBODIMENT

[0398] A semiconductor device of multilayer wiring structure using thelow dielectric thin film as an interlayer dielectric film will bedescribed as a fourteenth embodiment of the invention.

[0399] As shown in FIGS. 20A and 20B, the semiconductor device ischaracterized in that an interlayer dielectric film is formed from adielectric film of low dielectric constant having a cyclic porousstructure which includes poles provided in pores.

[0400] Here, the interlayer dielectric film is formed from a dielectricfilm of low dielectric constant which has a two-layer structure andincludes support members provided in pores as poles. As shown in FIG.21, the interlayer dielectric film is characterized in that the firstinterlayer dielectric film 13 a having the contact holes H that contactthe first wiring layer 12 is formed from the second porous structuredomain in which layered pores are arranged cyclically so as to becomeparallel with the surface of the substrate; and in that the secondinterlayer dielectric film 13 b—which is formed on the first interlayerdielectric film 13 a, serves as an upper layer portion, and is chargedinto areas between wiring patterns of the second wiring layer 14—isformed from the first porous structure domain, in which columnar poresare cyclically arranged in parallel with the surface of the substrate.

[0401] Specifically, a lower layer portion of the interlayer dielectricfilm—which is formed between the first wiring layer 12 formed on thesurface of an element region enclosed with the element isolationdielectric film (not shown) formed on the surface of the siliconsubstrate 11 and the second wiring layer 14—is taken as the firstinterlayer dielectric film 13 a in which layered pores are arrangedcyclically so as to become parallel with the surface of the substrate.The second interlayer dielectric film 13 b—which serves as an upperlayer portion and is formed in regions between wiring patterns of thesecond wiring layer as an inter-line dielectric film—is formed from thefirst porous structure domain in which columnar pores are arrangedcyclically.

[0402] The remaining portions of the semiconductor device are ofordinary structure, and their illustrations and explanations areomitted.

[0403] Processes for manufacturing the interlayer dielectric film willnow be described by reference to FIGS. 22A to 22D.

[0404] First, as shown in FIG. 22A, a desired semiconductor region isformed on the surface of a silicon substrate 11 by means of an ordinarymethod, thereby forming the first wiring layer.

[0405] Subsequently, by means of the method of the invention, amesoporous silica thin film is formed from a second cyclic porousstructure domain, wherein the layered pores are arranged cyclically soas to become parallel with the surface of the substrate, and a frameworksurrounding the pores is coated with a hydrophobic layer (FIG. 22B).

[0406] Specifically, as shown in FIG. 23A, cationic cetyltrimethylammonium bromide [CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] serving as a surface activeagent; tetramethoxy silane (TMOS) serving as a silica derivative; andhydrochloric acid (HCl) serving as an acid catalyst are dissolved intothe H₂O/alcohol mixed solvent, thereby preparing a precursor solutionwithin the mixing container. Mole ratios employed for preparing theprecursor solution are determined such that 0.5 parts surface activeagent, 5 parts silica derivative, and 2 parts acid catalyst are mixedtogether with the solution being taken as 100 parts. The substratehaving the first wiring layer 12 formed thereon is immersed in themixture of solutions. As shown in FIG. 3B, after the mixing containerhas been sealed, the mixture is maintained at 30° C. to 150° C. for oneto 120 hours, whereby the silica derivative is subjected topolymerization through hydrolysis polycondensation reaction (apreliminary crosslinking process), thereby forming a mesoporous silicathin film which takes a cyclic self-agglomerate of the surface activeagent as a mold.

[0407] As shown in FIG. 23A, the self-agglomerate forms a sphericalmicelle structure (FIG. 23B) into which a plurality of molecules, eachcomprising C₁₆H₃₃N⁺(CH₃)₃Br⁻, coagulate. There is formed a thin film oflaminated structure (FIG. 25A) in which the surface active agent isoriented as the density increases.

[0408] Subsequently, the substrate is immersed in a magnesium oxidesolution at 0 to 90° C. for a few seconds to five hours, wherebyportions of the surface active agent are replaced with ultrafinemagnesium particles through substitution. As shown in FIG. 25B, thepoles S of ultrafine magnesium-particles are formed. Here, a desirabletemperature is 20 to 30° C. The larger the particles employed forreplacement, the slower the particles diffuse. The smaller theparticles, the faster the particles diffuse. Hence, the time duringwhich the substrate is to be immersed must be controlled in accordancewith particle size. Diffusion has relatively low dependence ontemperature, but reaction is highly dependent on temperature.

[0409] The substrate is raised and subjected to rinsing and drying.Subsequently, the substrate is heated and sintered for three hours in anitrogen atmosphere at 400° C., thereby completely removing the surfaceactive agent remaining in the mold through thermal decomposition. Asshown in FIG. 25C, a pure mesoporous silica thin film having the poles Sis formed. Here, the geometry of the poles can be changed as required;for instance, flat ultrafine particles or normal chain clusters can beproduced.

[0410] In this way, as shown in FIG. 22B, the first interlayerdielectric film 13 a is formed.

[0411] As shown in FIG. 22C, the through holes H are formed in the firstinterlayer dielectric film 13 a. By means of the normal method, thesecond wiring layer 14 is formed.

[0412] Subsequently, the second interlayer dielectric film 13 b isformed. The second interlayer dielectric film is formed in the samemanner as in the process for forming the first interlayer dielectricfilm 13 a. However, there is employed a precursor solution whosecomposition is changed from that of the precursor solution employed forforming the first interlayer dielectric film. Here, mole ratios employedfor preparing the precursor solution were determined such that 0.05parts surface active agent, 0.1 parts silica derivative, and 2 partsacid catalyst are mixed together with the solution being taken as 100parts. In other respects, the second interlayer dielectric film isformed in totally the same manner as that employed for forming the firstinterlayer dielectric film.

[0413] As shown in FIG. 22D, there is obtained the second interlayerdielectric film 13 b formed from the first porous structure domain,wherein columnar pores are cyclically arranged.

[0414] Here, as shown in FIG. 23A, the self-agglomerate forms aspherical micelle structure (FIG. 23B) into which a plurality ofmolecules, each comprising C₁₆H₃₃N⁺(CH₃)₃Br⁻, coagulate. There is formeda porous member (FIG. 23C) in which the surface active agent is orientedas the density increases. Portions of molecules of the surface activeagent are replaced with metal oxide precursors (containing Si and Ge)through substitution, thereby forming the poles S. As a result of themicelle structure having been sintered, there is formed an interlayerdielectric film in which pores having the poles S are arranged, as shownin FIG. 23E. Here, the poles (i.e., supports formed from columnarmembers) are not necessarily oriented.

[0415] The micelle structure, as shown in FIGS. 23D and 23F, iseffective and higher in mechanical strength than a structure in whichtwo poles are formed in one pore and sintered.

[0416]FIG. 24 is a structural descriptive view showing the cross sectionof the structure in this state. As is evident from the drawing, thestructure is understood to comprise the first interlayer dielectric film13 a in which pores are formed in a layered form and which is formedfrom a porous thin film having poles provided in pores, and the secondinterlayer dielectric film 13 b in which columnar pores are cyclicallyarranged and which has poles provided in pores.

[0417] In relation to the semiconductor device having the thus-formedmultilayer wiring structure, the interlayer dielectric film has atwo-layer structure formed from the first interlayer dielectric film andthe second interlayer dielectric film. The first interlayer dielectricfilm constitutes, in the region surrounding the contact holes H, thesecond porous structure domain in which the layered pores are arrangedcyclically. Hence, the interlayer capacitance can be diminished.Further, the columnar pores are arranged laterally in an upper-layerwiring region constituting an inter-line dielectric film. Hence, lateralcapacitance is lowered to a much greater extent. In the secondinterlayer dielectric film, the direction in which the columnar poresare arranged is parallel with the wiring direction of the second wiringlayer 14. Hence, a highly-reliable semiconductor device can be providedwithout involvement of occurrence of a short circuit between wires.

FIFTEENTH EMBODIMENT

[0418] FRAM using a low dielectric thin film as an interlayer dielectricfilm is described as a fifteenth embodiment of the invention.

[0419] As shown in FIG. 26A, the FRAM comprises a switching transistorfabricated in the element region enclosed with the element isolationdielectric film 2 formed on the surface of the silicon substrate 1, andthe ferroelectric capacitor. The invention is characterized by use ofthe thin film 7 of low dielectric constant of the invention as aninterlayer dielectric film between the switching transistor and thelower electrode 9 of the ferroelectric capacitor. As shown in anenlarged perspective view of the featured section shown in FIG. 26B, thelow dielectric thin film is characterized by comprising the first porousstructure domain 7 c which has supports S and in which columnar poresare arranged cyclically, and the second porous structure domain 7 swhich has the supports S in the direction differing from that of thefirst porous structure domain 7C and in which columnar pores arecyclically arranged in parallel with the surface of the substrate, whichare repeatedly laminated on the surface of the substrate.

[0420] By means of such a configuration, the mechanical strength can beimproved to a great extent. The pores can assume a closed structure inwhich no opening sections are provided for an upper layer wiring patternor a lower layer wiring pattern. Thus, the interlayer dielectric filmplays the role of a low dielectric thin film which has superior moistureresistance and extremely high reliability.

[0421] The other portions of the interlayer dielectric film are formedby means of the ordinary method. The switching transistor has a gateelectrode formed on the surface of the silicon substrate 1 by way of thegate dielectric film 3, and the source region 5 and the drain region 6formed such that the gate electrode is sandwiched therebetween. Thelower electrode 9 is connected to the drain region 6 by way of thecontact 8. Source and drain regions are connected to a bit line BL.

[0422] The ferroelectric capacitor is formed from a ferroelectric thinfilm 10 which is formed from a PZT between the lower electrode 9 and theupper electrode 11.

[0423] Processes for manufacturing the FRAM will be described byreference to FIGS. 8A to 8D that have been described in connection withthe third embodiment.

[0424] First, by means of the ordinary method, the gate electrode 4 isformed on the surface of the silicon substrate 1 by way of the gatedielectric film 3. The substrate is subjected to diffusion of impuritieswhile the gate electrode is taken as a mask, thereby forming the sourceregion 5 and the drain region 6 (FIG. 8A).

[0425] Subsequently, by means of the method of the invention, amesoporous silica thin film is formed to include a plurality of cyclicporous structure domains containing columnar pores oriented in onedirection so as to become parallel with the surface of the substrate(FIG. 8B).

[0426] Specifically, as shown in FIG. 8A, cationic cetyltrimethylammonium bromide [CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] serving as a surface activeagent; tetramethoxy silane (TMOS) serving as a silica derivative; andhydrochloric acid (HCl) serving as an acid catalyst are dissolved intoan H₂O/alcohol mixed solvent, thereby preparing a precursor solutionwithin a mixing container. Mole ratios employed for preparing theprecursor solution were determined such that 0.05 parts surface activeagent, 0.1 parts silica derivative, and 2 parts acid catalyst are mixedtogether with the solution being taken as 100 parts. Mole ratiosemployed for preparing the second precursor solution are determined suchthat 0.5 parts surface active agent, 5 parts silica derivative, and 2parts acid catalyst are mixed together with the solution being taken as100 parts. As shown in FIG. 9, the thus-formed first and secondprecursor solutions are dropped onto the surface of the substrate 1placed on a spinner by way of respective nozzles. The substrate is spunat 500 to 5000 rpm, to thus form a mesoporous silica thin film. Themesoporous silica thin film is maintained at 30° C. to 150° C. for oneto 120 hours, whereby the silica derivative is subjected topolymerization through hydrolysis polycondensation reaction (apreliminary crosslinking process), thereby forming a mesoporous silicathin film while a cyclic self-agglomerate of the surface active agent istaken as a mold. Here, the preliminary crosslinking process is performedpreferably at 60° C. to 120° C., more preferably at 70° C. to 90° C.,for about 12 to 72 hours.

[0427] Subsequently, the mesoporous silica thin film is brought intocontact with an alumina silica solution at 0° C. to 90° C., preferably,20° C. to 30° C., for several seconds to five hours. As a result,through substitution, portions of the surface active agent are replacedwith alumina ions, alumina molecules, an alumina polymer, or ultra finealumina particles, thereby forming supports.

[0428] Finally, as in the case of the fourteenth embodiment, thesubstrate is sintered so as to completely thermally decompose and removethe surface active agent, thus forming a pure mesoporous silica thinfilm.

[0429] In this way, as shown in FIGS. 26A and 26B, the thin film 7 oflow dielectric constant of the embodiment is formed. In fact, in orderto form a bit line BL, the low dielectric thin film must be formedtwice. An interlayer dielectric film of two-layer structure havingdifferent layouts of pores may be formed by use of precursor solutionsof different composition ratios before and after formation of the bitline BL.

[0430] In the embodiment, the substrate is subjected to preliminarycrosslinking after the precursor solution has been applied over thesurface of the substrate. However, the precursor solution may be appliedover the surface of the substrate after the substrate has been subjectedto crosslinking. By means of such a configuration, the precursorsolutions hardly become mixed together and can maintain their ownstates. For this reason, an interlayer dielectric film having aplurality of cyclic porous structures can be formed more easily.Moreover, productivity can be improved by means of preliminarycrosslinking.

[0431] Subsequently, by means of the ordinary method, contact holes 8are formed in the thin film 7 of low dielectric constant. After plugshave been formed by embedding a highly-doped polycrystalline siliconlayer in the respective contact holes, an iridium oxide layer is formedthrough use of a gas mixture consisting of argon and oxygen whileiridium is used as a target. A platinum layer is formed on the iridiumoxide layer while platinum is used as a target. In this way, as shown inFIG. 8C, the iridium oxide layer having a thickness of about 50 nm andthe platinum layer having a thickness of about 200 nm are formed. Theselayers are patterned through photolithography, to thereby form the lowerelectrodes 9.

[0432] A PZT film is formed on the lower electrodes 9 as theferroelectric film 10 by means of a sol-gel method. A mixed solution ofPb(CH₃COO)₂.3H₂O,Zr(t-OC₄H₉)₄,Ti(i-OC₃H₇)₄ is used as a startingmaterial. After the mixed solution has been applied over the substratethrough spin coating, the substrate is dried at 150° C. and subjected totemporal sintering for 30 minutes at 400° C. in a dry air atmosphere.After having been repeatedly subjected to these operations five times,the substrate is subjected to heat treatment at a temperature of 700° C.or greater in an O₂ atmosphere. Thus, the ferroelectric film 10 having athickness of 250 nm is formed. Here, the PZT film is formed while “x” inPbZr_(x)Ti_(1-x)O₃ is taken as 0.52 [hereinafter expressed as PZT(52/48)] (FIG. 8D).

[0433] The laminated film 11 consisting of iridium oxide and iridium isformed on the ferroelectric film 10 by means of sputtering. Thelaminated film consisting of an iridium oxide layer and an iridium layeris taken as an upper electrode 11. The iridium layer and the iridiumoxide layer are formed to a total thickness of 200 nm. Thus, aferroelectric capacitor can be obtained, and the FRAM shown in FIG. 26is formed.

[0434] By means of such a configuration, the interlayer dielectric filmis formed from a low dielectric thin film formed from the mesoporoussilica thin film. Hence, capacitance attributable to the interlayerdielectric film is diminished, and there can be formed FRAM whoseswitching characteristic is good and which can operate at high speed.

[0435] By employment of a cyclic porous structure, the mechanicalstrength of the dielectric film can be enhanced, and the dielectric filmhaving high reliability can be obtained. The first and second porousstructure domains in which columnar pores are cyclically arranged indifference directions are arranged repeatedly. Hence, the pores canassume a closed structure in which no opening sections are provided forthe upper and lower wiring. The interlayer dielectric film plays therole of a low dielectric thin film which has superior moistureresistance and high reliability. Accordingly, no leakage current arises,and the interlayer dielectric film has longer life.

[0436] The compositions of the first and second precursor solutions arenot limited to the compositions employed in the embodiment. Under theassumption that the solution assumes a value of 100, the surface activeagent preferably assumes a value of 0.01 to 0.1; the silica derivativepreferably assumes a value of 0.01 to 0.5; and the acid catalystpreferably assumes a value of 0 to 5. Use of the precursor solutionhaving the composition enables formation of a dielectric film of lowdielectric constant having columnar pores.

[0437] In the respective embodiments, the low dielectric film can be setso as to assume a pore ratio of 50% or higher.

[0438] In the embodiment, cationic cetyltrimethyl ammonium bromide[CTAB: C₁₆H₃₃N⁺(CH₃)₃Br⁻] is used as a surface active agent. It goeswithout saying that the surface active agent is not limited to such anagent, and another surface active agent may be employed.

[0439] Use of alkali ions, such as Na ions, as catalysts willdeteriorate a semiconductor material. Therefore, use of a cationicsurface active agent and use of an acid catalyst are preferable. Inaddition to HCl, nitric acid (HNO₃), sulfuric acid (H₂SO₄), phosphoricacid (H₃PO₄), H₄SO₄, or the like may also be used as the acid catalyst.

[0440] The silica derivative is not limited to TMOS. Silicon alkoxidematerial, such as tetraethoxy silane (TEOS), is preferably used.

[0441] Further, the water H₂O/alcohol mixed solvent is used as asolvent. However, it may be the case that only water is used.

[0442] Moreover, although the nitrogen atmosphere is used as a sinteringatmosphere, sintering is performed in preferably the atmosphere ofoxygen or may be performed in the atmosphere, under a reduced pressure,or in a nitrogen atmosphere. Preferably, additional sintering involvingusage of a foaming gas formed from a gas mixture consisting of nitrogenand hydrogen enhances moisture resistance, thereby enabling an attemptto reduce a leakage current.

[0443] A mixing ratio of the surface active agent, the silicaderivative, the acid catalyst, and the solvent can be changed asrequired.

[0444] The preliminary polymerization process is conducted at 30° C. to150° C. for one through 120 hours. The temperature is desirable set to60° C. to 120° C., more preferably to 90° C.

[0445] The sintering process is performed for one hour at 400° C.However, sintering may be performed at 300° C. to 500° C. from one tofive hours or thereabouts. Preferably, the temperature is set to 350° C.to 450° C.

[0446] At the time of formation of the poles, silanol molecules may beused in lieu of alumina. In this case, after the silica solution hasbeen heated and subjected to preliminary crosslinking, a solutioncontaining silanol molecules may be brought into contact with the silicasolution, to thereby replace alumina with silanol molecules throughsubstitution.

[0447] As shown in FIG. 12, a structure—including a regular arrangementof a porous structure domain having the poles S provided in the layeredpores formed in parallel with the surface of the substrate and a porousstructure domain having the poles S provided in the layered pores formedat right angles to the surface of the substrate—is also effective as amodification of the dielectric film of low dielectric constant.

[0448] As shown in FIG. 27, a structure—including a regular arrangementof the porous structure domain having the poles S provided in thelayered pores formed in parallel with the surface of the substrate and aporous structure domain having one or two poles provided inperiodically-arranged columnar pores—is also effective as a modificationof the dielectric film of low dielectric constant.

[0449] As shown in FIG. 14, a structure—in which there coexist, indifferent directions within a plane, a porous structure domain havingthe poles S provided in the layered pores formed in parallel with thesurface of the substrate and a porous structure domain having the polesprovided in periodically-arranged columnar pores; that is, a structureshown in FIG. 28—is also effective as a modification of the dielectricfilm of low dielectric constant.

[0450] As shown in FIG. 15, a so-called amorphous porous structure—inwhich the pores having the poles S are arranged at random—is alsoeffective as a modification of the dielectric film of low dielectricconstant.

[0451] In addition, the embodiments have described the interlayerdielectric film of FRAM. However, the invention can also be applied tosilicon devices such as bipolar devices, BiCMOSs, or CMOSs; otherhigh-speed devices such as HEMTs; high-frequency devices such asmicrowave ICs; and highly-integrated ferroelectric memory of MNMIS type.

[0452] Industrial Applicability

[0453] As has been described, the invention can provide a dielectricfilm having enhanced mechanical strength and a low dielectric constant.

[0454] An effective low dielectric thin film can be obtained as,particularly, an interlayer dielectric film.

1. A semiconductor device comprising: an inorganic dielectric film whichis formed on the surface of a substrate and has a pore ratio of 50% orhigher.
 2. The semiconductor device according to claim 1, wherein theinorganic dielectric film is formed on the surface of the substrate, andthe pores have an orientation characteristic.
 3. The semiconductordevice according to claim 1, further comprising: an inorganic dielectricfilm which is formed on the surface of the substrate and has periodicporous structures of two or more types.
 4. The semiconductor deviceaccording to claim 1, wherein the inorganic film has a first porousstructure domain having periodically-arranged columnar pores, and asecond porous structure domain having layered pores periodicallyarranged in a direction perpendicular to the surface of the substrate.5. The semiconductor device according to claim 1, wherein the inorganicdielectric film is formed by repeatedly laminating, on and in parallelwith the surface of the substrate, a first porous structure domain layerin which columnar pores are arranged cyclically, and a second porousstructure domain in which layered pores are cyclically arranged inparallel with the surface of the substrate.
 6. The semiconductor deviceaccording to claim 1, wherein the inorganic dielectric film comprises asemiconductor substrate or a first layer wiring conductor formed on thesurface of the semiconductor substrate, and an interlayer dielectricfilm interposed between the semiconductor substrate or the first layerwiring conductor and a second layer wiring conductor formed thereon. 7.The semiconductor device according to claim 6, wherein the interlayerdielectric film comprises a first interlayer dielectric film which isformed on the first layer wiring conductor and has contact holes tocontact the first layer wiring conductor, and a second interlayerdielectric film to be charged into an inter-wiring area of a secondlayer wiring conductor formed on the first interlayer dielectric film;and the first interlayer dielectric film is formed from a second porousstructure domain in which layered pores are arranged cyclically.
 8. Thesemiconductor device according to claim 6, wherein the interlayerdielectric film comprises a first interlayer dielectric film which isformed on the first layer wiring conductor and has contact holes tocontact the first layer wiring conductor, and a second interlayerdielectric film to be charged into an inter-wiring area of a secondlayer wiring conductor formed on the first interlayer dielectric film;the first interlayer dielectric film is formed from a second porousstructure domain in which layered pores are arranged cyclically; and thesecond interlayer dielectric film is formed from a first porousstructure domain in which columnar pores are arranged cyclically.
 9. Thesemiconductor device according to claim 4, wherein the interlayerdielectric film comprises a first interlayer dielectric film which isformed on the first layer wiring conductor and has contact holes tocontact the first layer wiring conductor, and a second interlayerdielectric film to be charged into an inter-wiring area of a secondlayer wiring conductor formed on the first interlayer dielectric film;the first interlayer dielectric film is formed from a second porousstructure domain in which layered pores formed so as to become parallelwith the surface of the substrate are arranged cyclically; and thesecond interlayer dielectric film is formed from a third porousstructure domain in which layered pores formed so as to becomesubstantially perpendicular to the surface of the substrate are arrangedcyclically.
 10. A method for manufacturing a semiconductor device,comprising: a process of producing a first precursor solution containinga silica derivative and a surface active agent so as to assume a firstcomposition ratio at which pores are arranged cyclically; a process ofproducing a second precursor solution containing a silica derivative anda surface active agent so as to assume a second composition ratio atwhich pores are arranged cyclically; a preliminary crosslinking processwhich raises the temperature of the first precursor solution and that ofthe second precursor solution, to thus initiate a crosslinking reaction;a contact process for bringing into contact with the surface of thesubstrate the first and second precursor solutions that have started thecrosslinking reaction in the preliminary crosslinking process; and aprocess for sintering the substrate with which the first and secondprecursor solutions have been brought into contact, in order todecompose and remove the surface active agent, whereby a dielectric filmis formed.
 11. A method for manufacturing a semiconductor device,comprising: a process of producing a first precursor solution containinga silica derivative and a surface active agent so as to assume a firstcomposition ratio at which pores are arranged cyclically; a process ofproducing a second precursor solution containing a silica derivative anda surface active agent so as to assume a second composition ratio atwhich pores are arranged cyclically; a contact process for bringing thefirst and second precursor solutions into contact with the surface ofthe substrate; a preliminary crosslinking process for heating thesubstrate with which the first and second precursor solutions have beenbrought into contact, to thus initiate a crosslinking reaction; and aprocess for sintering the substrate in order to decompose and remove thesurface active agent, whereby a dielectric film is formed.
 12. Themethod for manufacturing a semiconductor device according to claim 10,wherein the contact process is a process for sequentially and repeatedlyimmersing the substrate into the first and second precursor solutions.13. The method for manufacturing a semiconductor device according toclaim 10, wherein the contact process includes a process for immersingthe substrate into the first precursor solution and raising thesubstrate at a desired speed, and a process for immersing the substrateinto the second precursor solution and raising the substrate at adesired speed.
 14. The method for manufacturing a semiconductor deviceaccording to claim 10, wherein the contact process is a process forsequentially and repeatedly applying the first and second precursorsolutions over the substrate.
 15. The method for manufacturing asemiconductor device according to claim 10, wherein the contact processis a spin coating process for dropping the first and second precursorsolutions on the substrate and spinning the substrate.
 16. Thesemiconductor device according to claim 1, wherein the inorganicdielectric film is formed on the surface of the substrate and has acyclic porous structure including columnar pores oriented so as tobecome parallel with the surface of the substrate.
 17. The semiconductordevice according to claim 1, wherein the inorganic dielectric film isformed on the surface of the substrate and includes a plurality ofcyclic porous structure domains containing columnar pores oriented inone direction so as to become parallel with the surface of thesubstrate; and adjacent porous structure domains are oriented indifferent directions.
 18. The semiconductor device according to claim 1,wherein the inorganic dielectric film is formed on the surface of thesubstrate and has a cyclic porous structure domain in which layeredpores are oriented cyclically in one direction so as to become parallelwith the surface of the substrate.
 19. A method for manufacturing asemiconductor device, comprising: a process of producing a precursorsolution containing a silica derivative and a surface active agent; acontact process for bringing the precursor solution into contact withthe surface of the substrate; and a process for sintering the substratewith which the precursor solution has been brought into contact, inorder to decompose and remove the surface active agent, whereby adielectric film is formed.
 20. The method for manufacturing asemiconductor device according to claim 19, further comprising apreliminary crosslinking process, preceding the contact process, forraising the temperature of the precursor solution in order to initiate acrosslinking reaction.
 21. The method for manufacturing a semiconductordevice according to claim 19, wherein the contact process is a processfor applying the precursor solution over the substrate.
 22. The methodfor manufacturing a semiconductor device according to claim 19, whereinthe contact process is a spin coating process for dropping the precursorsolution on the substrate and spinning the substrate.
 23. Thesemiconductor device according to claim 1, further comprising aninorganic dielectric film which is formed on the surface of thesubstrate and has a porous structure whose framework surrounds pores andis coated with a hydrophobic layer.
 24. A method for manufacturing asemiconductor device, comprising: a process of producing a precursorsolution containing a silica derivative and a surface active agent; acontact process for bringing the precursor solution into contact withthe surface of the substrate; a process for sintering the substrate withwhich the precursor solution has been brought into contact, to therebydecompose and remove the surface active agent; and a process forsubjecting a silica thin film of porous structure obtained in thedecomposition removal process to hydrophobic treatment, thereby forminga dielectric film of porous structure having a framework whose surfaceis coated with a hydrophobic layer.
 25. The method for manufacturing asemiconductor device according to claim 24, wherein the hydrophobictreatment process is a sililation process.
 26. The semiconductor deviceaccording to claim 1, further comprising an inorganic dielectric filmwhich is formed on the surface of the substrate and has a porousstructure having pores constituting a three-dimensional network.
 27. Thesemiconductor device according to claim 26, wherein the inorganicdielectric film has a porous structure having pores constituting aperiodic three-dimensional network.
 28. The semiconductor deviceaccording to claim 1, further comprising an inorganic dielectric filmwhich is formed on the surface of the substrate and which has a porousstructure containing at least one support member in the pore.
 29. Thesemiconductor device according to claim 28, wherein the inorganicdielectric film is formed on the surface of the substrate, and the porespossess an orientation characteristic.
 30. The semiconductor deviceaccording to claim 28, wherein the inorganic dielectric film is formedon the surface of the substrate and has columnar pores, as well as acyclic porous structure including support members arranged within thecolumnar pore so as to extend across the diameter of a bottom surfacethereof.
 31. The semiconductor device according to claim 28, wherein theinorganic dielectric film is formed on the surface of the substrate andhas columnar pores oriented so as to become parallel with the surface ofthe substrate, and a cyclic porous structure including support membersarranged within the columnar pore so as to extend across the diameter ofa bottom surface thereof.
 32. The semiconductor device according toclaim 28, wherein the inorganic dielectric film is formed on the surfaceof the substrate and has layered pores and a cyclic porous structureincluding a columnar member arranged in the layered pore so as tosupport an interlayer space.
 33. The semiconductor device according toclaim 32, wherein the inorganic dielectric film is formed on the surfaceof the substrate and includes layered pores oriented so as to becomeparallel with the surface of the substrate.
 34. The semiconductor deviceaccording to claim 28, wherein the inorganic dielectric film comprises asemiconductor substrate or a lower layer wiring conductor formedthereon, and an interlayer dielectric film interposed between thesemiconductor substrate or the lower layer wiring conductor and an upperlayer wiring conductor.
 35. A method for manufacturing a semiconductordevice, comprising: a process of producing a precursor solutioncontaining a silica derivative and a surface active agent; a contactprocess for bringing the precursor solution into contact with thesurface of the substrate; a substitution process for replacing, throughsubstitution, at least a portion of the surface active agent of theprecursor solution with a compound constituting a support member ofmolecular size; and a process for sintering the substrate in order todecompose and remove the surface active agent, whereby a dielectric filmis formed.
 36. A method for manufacturing a semiconductor device,comprising: a process of producing a precursor solution containing asilica derivative and a surface active agent; a preliminary crosslinkingprocess which raises the temperature of the precursor solution, to thusinitiate a crosslinking reaction; a contact process for bringing intocontact with the surface of the substrate the precursor solution thathas started the crosslinking reaction in the preliminary crosslinkingprocess; a substitution process for replacing, through substitution, atleast a portion of the surface active agent of the precursor solutionwith a compound constituting a support member of molecular size; and aprocess for sintering the substrate in order to decompose and remove thesurface active agent, whereby a dielectric film is formed.
 37. Themethod for manufacturing a semiconductor device according to claim 36,wherein the substitution process is a process for replacing at least aportion of the surface active agent with an organic molecule.
 38. Themethod for manufacturing a semiconductor device according to claim 36,wherein the substitution process is a process for replacing at least aportion of the surface active agent with an inorganic molecule.
 39. Themethod for manufacturing a semiconductor device according to claim 37,wherein the substitution process is a process for replacing the surfaceactive agent with superfine particles of an inorganic compound.
 40. Themethod for manufacturing a semiconductor device according to claim 37,wherein the inorganic compound is hydrated magnesia (MgO)_(m)(H₂O)_(n).41. The method for manufacturing a semiconductor device according toclaim 36, wherein the substitution process is a process for growing theinorganic compound molecules in a pore through diffusion.
 42. The methodfor manufacturing a semiconductor device according to claim 36, whereinthe substitution process is a process for replacing, throughsubstitution, a single or a plurality of straight chain silanolmolecules produced by hydrolysis polycondensation reaction ofsilicon-hydroxide-based molecules.
 43. A semiconductor devicecomprising: an inorganic film which is formed on the surface of asubstrate and has cyclic porous structures of two or more types.
 44. Asemiconductor device comprising: an inorganic film which is formed onthe surface of a substrate and has a porous structure having a frameworkwhich surrounds pores and is coated with a hydrophobic layer.
 45. Asemiconductor device comprising: an inorganic film which is formed onthe surface of a substrate and has a porous structure including poresconstituting a three-dimensional network.
 46. A semiconductor devicecomprising: an inorganic dielectric film of porous structure which isformed on the surface of the substrate and in which at least one supportmember is included in a pore.
 47. The method for manufacturing asemiconductor device according to claim 11, wherein the contact processis a process for sequentially and repeatedly immersing the substrateinto the first and second precursor solutions.
 48. The method formanufacturing a semiconductor device according to claim 11, wherein thecontact process includes a process for immersing the substrate into thefirst precursor solution and raising the substrate at a desired speed,and a process for immersing the substrate into the second precursorsolution and raising the substrate at a desired speed.
 49. The methodfor manufacturing a semiconductor device according to claim 11, whereinthe contact process is a process for sequentially and repeatedlyapplying the first and second precursor solutions over the substrate.50. The method for manufacturing a semiconductor device according toclaim 11, wherein the contact process is a spin coating process fordropping the first and second precursor solutions on the substrate andspinning the substrate.